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2 <p>Last updated on<strong>August 5, 2025</strong></p>

3 <p>The product of multiplying an integer by itself is the square of a number. Square is used in programming, calculating areas, and so on. In this topic, we will discuss the square of -21.</p>

4 <h2>What is the Square of -21</h2>

5 <p>The<a>square</a>of a<a>number</a>is the<a>product</a>of the number itself. The square of -21 is (-21) × (-21). The square of a number always ends in 0, 1, 4, 5, 6, or 9. We write it in<a>math</a>as (-21)², where -21 is the<a>base</a>and 2 is the<a>exponent</a>. The square of a positive and a<a>negative number</a>is always positive. For example, 5² = 25; (-5)² = 25.</p>

6 <p><strong>The square of -21</strong>is (-21) × (-21) = 441.</p>

7 <p><strong>Square of -21 in exponential form:</strong>(-21)²</p>

8 <p><strong>Square of -21 in arithmetic form:</strong>(-21) × (-21)</p>

9 <h2>How to Calculate the Value of Square of -21</h2>

10 <p>The square of a number is multiplying the number by itself. So let’s learn how to find the square of a number. These are the common methods used to find the square of a number.</p>

11 <ol><li>By Multiplication Method</li>

12 <li>Using a Formula</li>

13 <li>Using a Calculator</li>

14 </ol><h2>By the Multiplication method</h2>

15 <p>In this method, we will multiply the number by itself to find the square. The product here is the square of the number. Let’s find the square of -21.</p>

16 <p><strong>Step 1:</strong>Identify the number. Here, the number is -21</p>

17 <p><strong>Step 2:</strong>Multiplying the number by itself, we get, (-21) × (-21) = 441.</p>

18 <p>The square of -21 is 441.</p>

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21 <h2>Using a Formula (a²)</h2>

20 <h2>Using a Formula (a²)</h2>

22 <p>In this method, the<a>formula</a>, a² is used to find the square of the number. Where a is the number.</p>

21 <p>In this method, the<a>formula</a>, a² is used to find the square of the number. Where a is the number.</p>

23 <p><strong>Step 1:</strong>Understanding the<a>equation</a>Square of a number = a²</p>

22 <p><strong>Step 1:</strong>Understanding the<a>equation</a>Square of a number = a²</p>

24 <p>a² = a × a</p>

23 <p>a² = a × a</p>

25 <p><strong>Step 2:</strong>Identifying the number and substituting the value in the equation.</p>

24 <p><strong>Step 2:</strong>Identifying the number and substituting the value in the equation.</p>

26 <p>Here, ‘a’ is -21 So: (-21)² = (-21) × (-21) = 441</p>

25 <p>Here, ‘a’ is -21 So: (-21)² = (-21) × (-21) = 441</p>

27 <h2>By Using a Calculator</h2>

26 <h2>By Using a Calculator</h2>

28 <p>Using a<a>calculator</a>to find the square of a number is the easiest method. Let’s learn how to use a calculator to find the square of -21.</p>

27 <p>Using a<a>calculator</a>to find the square of a number is the easiest method. Let’s learn how to use a calculator to find the square of -21.</p>

29 <p><strong>Step 1:</strong>Enter the number in the calculator Enter -21 in the calculator.</p>

28 <p><strong>Step 1:</strong>Enter the number in the calculator Enter -21 in the calculator.</p>

30 <p><strong>Step 2:</strong>Multiply the number by itself using the<a>multiplication</a>button (×) That is (-21) × (-21)</p>

29 <p><strong>Step 2:</strong>Multiply the number by itself using the<a>multiplication</a>button (×) That is (-21) × (-21)</p>

31 <p><strong>Step 3:</strong>Press the equal to button to find the answer Here, the square of -21 is 441.</p>

30 <p><strong>Step 3:</strong>Press the equal to button to find the answer Here, the square of -21 is 441.</p>

32 <p><strong>Tips and Tricks for the Square of -21:</strong>Tips and tricks make it easy for students to understand and learn the square of a number. To master the square of a number, these tips and tricks will help students.</p>

31 <p><strong>Tips and Tricks for the Square of -21:</strong>Tips and tricks make it easy for students to understand and learn the square of a number. To master the square of a number, these tips and tricks will help students.</p>

33 <ul><li>The square of an<a>even number</a>is always an even number. For example, 6² = 36</li>

32 <ul><li>The square of an<a>even number</a>is always an even number. For example, 6² = 36</li>

34 </ul><ul><li>The square of an<a>odd number</a>is always an odd number. For example, 5² = 25</li>

33 </ul><ul><li>The square of an<a>odd number</a>is always an odd number. For example, 5² = 25</li>

35 </ul><ul><li>The last digit of the square of a number is always 0, 1, 4, 5, 6, or 9.</li>

34 </ul><ul><li>The last digit of the square of a number is always 0, 1, 4, 5, 6, or 9.</li>

36 </ul><ul><li>If the<a>square root</a>of a number is a<a>fraction</a>or a<a>decimal</a>, then the number is not a perfect square. For example, √1.44 = 1.2</li>

35 </ul><ul><li>If the<a>square root</a>of a number is a<a>fraction</a>or a<a>decimal</a>, then the number is not a perfect square. For example, √1.44 = 1.2</li>

37 </ul><ul><li>The square root of a perfect square is always a whole number. For example, √144 = 12.</li>

36 </ul><ul><li>The square root of a perfect square is always a whole number. For example, √144 = 12.</li>

38 </ul><h2>Common Mistakes to Avoid When Calculating the Square of -21</h2>

37 </ul><h2>Common Mistakes to Avoid When Calculating the Square of -21</h2>

39 <p>Mistakes are common among kids when doing math, especially when it is finding the square of a number. Let’s learn some common mistakes to master the squaring of a number.</p>

38 <p>Mistakes are common among kids when doing math, especially when it is finding the square of a number. Let’s learn some common mistakes to master the squaring of a number.</p>

40 <h3>Problem 1</h3>

39 <h3>Problem 1</h3>

41 <p>Find the length of the square, where the area of the square is 441 cm².</p>

40 <p>Find the length of the square, where the area of the square is 441 cm².</p>

42 <p>Okay, lets begin</p>

41 <p>Okay, lets begin</p>

43 <p>The area of a square = a²</p>

42 <p>The area of a square = a²</p>

44 <p>So, the area of a square = 441 cm²</p>

43 <p>So, the area of a square = 441 cm²</p>

45 <p>So, the length = √441 = 21.</p>

44 <p>So, the length = √441 = 21.</p>

46 <p>The length of each side = 21 cm</p>

45 <p>The length of each side = 21 cm</p>

47 <h3>Explanation</h3>

46 <h3>Explanation</h3>

48 <p>The length of a square is 21 cm. Because the area is 441 cm² the length is √441 = 21.</p>

47 <p>The length of a square is 21 cm. Because the area is 441 cm² the length is √441 = 21.</p>

49 <p>Well explained 👍</p>

48 <p>Well explained 👍</p>

50 <h3>Problem 2</h3>

49 <h3>Problem 2</h3>

51 <p>Tom is planning to paint his square wall of length -21 feet. The cost to paint a foot is 3 dollars. Can he paint the wall?</p>

50 <p>Tom is planning to paint his square wall of length -21 feet. The cost to paint a foot is 3 dollars. Can he paint the wall?</p>

52 <p>Okay, lets begin</p>

51 <p>Okay, lets begin</p>

53 <p>The length of the wall = 21 feet</p>

52 <p>The length of the wall = 21 feet</p>

54 <p>The cost to paint 1 square foot of wall = 3 dollars.</p>

53 <p>The cost to paint 1 square foot of wall = 3 dollars.</p>

55 <p>To find the total cost to paint, we find the area of the wall,</p>

54 <p>To find the total cost to paint, we find the area of the wall,</p>

56 <p>Area of the wall = area of the square = a²</p>

55 <p>Area of the wall = area of the square = a²</p>

57 <p>Here a = 21</p>

56 <p>Here a = 21</p>

58 <p>Therefore, the area of the wall = 21² = 21 × 21 = 441.</p>

57 <p>Therefore, the area of the wall = 21² = 21 × 21 = 441.</p>

59 <p>The cost to paint the wall = 441 × 3 = 1323.</p>

58 <p>The cost to paint the wall = 441 × 3 = 1323.</p>

60 <p>The total cost = 1323 dollars</p>

59 <p>The total cost = 1323 dollars</p>

61 <h3>Explanation</h3>

60 <h3>Explanation</h3>

62 <p>To find the cost to paint the wall, we multiply the area of the wall by cost to paint per foot. So, the total cost is 1323 dollars.</p>

61 <p>To find the cost to paint the wall, we multiply the area of the wall by cost to paint per foot. So, the total cost is 1323 dollars.</p>

63 <p>Well explained 👍</p>

62 <p>Well explained 👍</p>

64 <h3>Problem 3</h3>

63 <h3>Problem 3</h3>

65 <p>Find the area of a circle whose radius is 21 meters.</p>

64 <p>Find the area of a circle whose radius is 21 meters.</p>

66 <p>Okay, lets begin</p>

65 <p>Okay, lets begin</p>

67 <p>The area of the circle = 1,385.44 m²</p>

66 <p>The area of the circle = 1,385.44 m²</p>

68 <h3>Explanation</h3>

67 <h3>Explanation</h3>

69 <p>The area of a circle = πr²</p>

68 <p>The area of a circle = πr²</p>

70 <p>Here, r = 21</p>

69 <p>Here, r = 21</p>

71 <p>Therefore, the area of the circle = π × 21² = 3.14 × 21 × 21 = 1,385.44 m².</p>

70 <p>Therefore, the area of the circle = π × 21² = 3.14 × 21 × 21 = 1,385.44 m².</p>

72 <p>Well explained 👍</p>

71 <p>Well explained 👍</p>

73 <h3>Problem 4</h3>

72 <h3>Problem 4</h3>

74 <p>The area of the square is 441 cm². Find the perimeter of the square.</p>

73 <p>The area of the square is 441 cm². Find the perimeter of the square.</p>

75 <p>Okay, lets begin</p>

74 <p>Okay, lets begin</p>

76 <p>The perimeter of the square is 84 cm.</p>

75 <p>The perimeter of the square is 84 cm.</p>

77 <h3>Explanation</h3>

76 <h3>Explanation</h3>

78 <p>The area of the square = a²</p>

77 <p>The area of the square = a²</p>

79 <p>Here, the area is 441 cm²</p>

78 <p>Here, the area is 441 cm²</p>

80 <p>The length of the side is √441 = 21</p>

79 <p>The length of the side is √441 = 21</p>

81 <p>Perimeter of the square = 4a</p>

80 <p>Perimeter of the square = 4a</p>

82 <p>Here, a = 21</p>

81 <p>Here, a = 21</p>

83 <p>Therefore, the perimeter = 4 × 21 = 84.</p>

82 <p>Therefore, the perimeter = 4 × 21 = 84.</p>

84 <p>Well explained 👍</p>

83 <p>Well explained 👍</p>

85 <h3>Problem 5</h3>

84 <h3>Problem 5</h3>

86 <p>Find the square of -22.</p>

85 <p>Find the square of -22.</p>

87 <p>Okay, lets begin</p>

86 <p>Okay, lets begin</p>

88 <p>The square of -22 is 484.</p>

87 <p>The square of -22 is 484.</p>

89 <h3>Explanation</h3>

88 <h3>Explanation</h3>

90 <p>The square of -22 is multiplying -22 by -22. So, the square = (-22) × (-22) = 484</p>

89 <p>The square of -22 is multiplying -22 by -22. So, the square = (-22) × (-22) = 484</p>

91 <p>Well explained 👍</p>

90 <p>Well explained 👍</p>

92 <h2>FAQs on Square of -21</h2>

91 <h2>FAQs on Square of -21</h2>

93 <h3>1.What is the square of -21?</h3>

92 <h3>1.What is the square of -21?</h3>

94 <p>The square of -21 is 441, as (-21) × (-21) = 441.</p>

93 <p>The square of -21 is 441, as (-21) × (-21) = 441.</p>

95 <h3>2.What is the square root of 441?</h3>

94 <h3>2.What is the square root of 441?</h3>

96 <p>The square root of 441 is ±21.</p>

95 <p>The square root of 441 is ±21.</p>

97 <h3>3.Is -21 a perfect square?</h3>

96 <h3>3.Is -21 a perfect square?</h3>

98 <h3>4.What are the first few multiples of 21?</h3>

97 <h3>4.What are the first few multiples of 21?</h3>

99 <p>The first few<a>multiples</a>of 21 are 21, 42, 63, 84, 105, 126, 147, 168, and so on.</p>

98 <p>The first few<a>multiples</a>of 21 are 21, 42, 63, 84, 105, 126, 147, 168, and so on.</p>

100 <h3>5.What is the square of 20?</h3>

99 <h3>5.What is the square of 20?</h3>

101 <h2>Important Glossaries for Square of -21.</h2>

100 <h2>Important Glossaries for Square of -21.</h2>

102 <ul><li><strong>Perfect square:</strong>A number that is the square of an integer. For example, 1, 4, 9, 16, 25, etc.</li>

101 <ul><li><strong>Perfect square:</strong>A number that is the square of an integer. For example, 1, 4, 9, 16, 25, etc.</li>

103 </ul><ul><li><strong>Exponent:</strong>The exponent of a number shows how many times the number is multiplied by itself. For example, in 3², 2 is the exponent.</li>

102 </ul><ul><li><strong>Exponent:</strong>The exponent of a number shows how many times the number is multiplied by itself. For example, in 3², 2 is the exponent.</li>

104 </ul><ul><li><strong>Square root:</strong>The square root is the inverse operation of squaring a number. The square root of a number is a number whose square is the number itself.</li>

103 </ul><ul><li><strong>Square root:</strong>The square root is the inverse operation of squaring a number. The square root of a number is a number whose square is the number itself.</li>

105 </ul><ul><li><strong>Multiplication:</strong>An arithmetic operation that combines groups of equal sizes.</li>

104 </ul><ul><li><strong>Multiplication:</strong>An arithmetic operation that combines groups of equal sizes.</li>

106 </ul><ul><li><strong>Integer:</strong>A whole number that can be positive, negative, or zero.</li>

105 </ul><ul><li><strong>Integer:</strong>A whole number that can be positive, negative, or zero.</li>

107 </ul><p>What Is Algebra? 🧮 | Simple Explanation with 🎯 Cool Examples for Kids | ✨BrightCHAMPS Math</p>

106 </ul><p>What Is Algebra? 🧮 | Simple Explanation with 🎯 Cool Examples for Kids | ✨BrightCHAMPS Math</p>

108 <p>▶</p>

107 <p>▶</p>

109 <h2>Jaskaran Singh Saluja</h2>

108 <h2>Jaskaran Singh Saluja</h2>

110 <h3>About the Author</h3>

109 <h3>About the Author</h3>

111 <p>Jaskaran Singh Saluja is a math wizard with nearly three years of experience as a math teacher. His expertise is in algebra, so he can make algebra classes interesting by turning tricky equations into simple puzzles.</p>

110 <p>Jaskaran Singh Saluja is a math wizard with nearly three years of experience as a math teacher. His expertise is in algebra, so he can make algebra classes interesting by turning tricky equations into simple puzzles.</p>

112 <h3>Fun Fact</h3>

111 <h3>Fun Fact</h3>

113 <p>: He loves to play the quiz with kids through algebra to make kids love it.</p>

112 <p>: He loves to play the quiz with kids through algebra to make kids love it.</p>