Class 8 Notes - Squares and Square Roots
Introduction
The chapter "Squares and Square Roots" explores the concepts of squaring a number and finding its square root. These concepts are fundamental in understanding further mathematical topics such as algebra, geometry, and higher arithmetic.
1. Perfect Squares
Definition:
A number is called a perfect square if it is the square of an integer.
Examples: 1 = 1², 4 = 2², 9 = 3², 16 = 4², 25 = 5²
Properties of Perfect Squares:
- A perfect square ends in 0, 1, 4, 5, 6, or 9. It never ends in 2, 3, 7, or 8.
- The square of an even number is always even.
- The square of an odd number is always odd.
- The number of zeros at the end of a perfect square is always even.
- The square of a number n is always greater than or equal to n.
2. Patterns in Square Numbers
a) Sum of first n odd numbers:
1 + 3 + 5 + ... + (2n - 1) = n²
Example:
1 + 3 = 4 = 2²
1 + 3 + 5 = 9 = 3²
b) Numbers between square numbers:
Between two consecutive squares n² and (n+1)², there are 2n numbers.
c) Square of numbers ending with 5:
If a number ends in 5, say 25:
25² = (2 × 3) followed by 25 = 625
3. Properties of Square Numbers
If a number is a perfect square, then in its prime factorization, each prime number appears an even number of times.
Example:
144 = 2⁴ × 3² ⇒ Perfect square
4. Square Root
Definition:
The square root of a number x is a number y such that y² = x. We write y = √x.
√49 = 7, √100 = 10
5. Methods to Find Square Roots
a) Prime Factorization Method:
- Find prime factors.
- Group identical pairs.
- Take one from each pair and multiply.
√324 = 2² × 3⁴ ⇒ √324 = 2 × 9 = 18
b) Estimation Method:
Estimate square root by identifying nearest perfect squares.
√50 ≈ 7.07 (since 7² = 49 and 8² = 64)
c) Long Division Method:
Used for large numbers or decimals. Divide in pairs and apply the square root rule as in long division.
√2025 = 45 (by long division method)
6. Square Roots of Decimals
- Make number of decimal digits even.
- Use long division method.
- Place decimal in the square root accordingly.
√2.25 = 1.5
7. Square Roots of Fractions
For a fraction a/b: √(a/b) = √a / √b
√(49/64) = 7/8
8. Some Important Square Roots
| Number |
Square |
Square Root |
| 1 | 1 | 1 |
| 2 | 4 | 2 |
| 3 | 9 | 3 |
| 4 | 16 | 4 |
| 5 | 25 | 5 |
| 6 | 36 | 6 |
| 7 | 49 | 7 |
| 8 | 64 | 8 |
| 9 | 81 | 9 |
| 10 | 100 | 10 |
| 11 | 121 | 11 |
| 12 | 144 | 12 |
| 13 | 169 | 13 |
| 14 | 196 | 14 |
| 15 | 225 | 15 |
9. Pythagorean Triplets
A triplet (a, b, c) where a² + b² = c²
Example: 3² + 4² = 9 + 16 = 25 = 5²
Formula: For n > 1: (2n, n²−1, n²+1)
n = 3 ⇒ (6, 8, 10)
10. Applications in Real Life
- Geometry (diagonals, area)
- Construction and Architecture
- Physics (energy, velocity)
- Computer Graphics (distances)
- Finance (standard deviation)
11. Solved Examples
Example 1: Is 784 a perfect square?
784 = 2⁴ × 7² ⇒ √784 = 2² × 7 = 4 × 7 = 28
Example 2: Find smallest number to multiply 180 to make it a perfect square.
180 = 2² × 3² × 5 ⇒ Multiply by 5
12. Practice Questions
- Find the square root of:
- Is 105 a perfect square?
- Find the smallest number that must be divided into 3600 to make it a perfect square.
- Use long division method to find:
- Form a Pythagorean triplet using n = 6.
Conclusion
Understanding the chapter "Squares and Square Roots" builds a strong foundation for algebraic and geometric concepts. Students should focus on identifying patterns, using suitable methods to calculate square roots, and applying the knowledge in real-world problems.
Consistent practice with factorization, long division, and estimation will help develop accuracy and confidence.