Question

Verify 1) x³+y³=(x+y)(x²-xy+y²)

2) x³-y³=(x-y)(x²+xy+y²)
using some non-zero positive integers and check by actual multiplication. can you call these as identities? ​

Answer 1

To Prove & verify that :

x³ + y³ = (x + y)(x² - xy + y²)

x³ - y³ = (x - y)(x² + xy + y²).

Proof for 1st Identity :

★ x³ + y³ = x (x² - xy + y²) + y(x² - xy + y²)

⟶ x³ + y³ = x³ - x²y + xy² + x²y - xy² + y³

⟶ x³ + y³ = x³ + y³

Proof for 2nd identity :

★ x³ - y³ = x(x² + xy + y²) - y(x² + xy + y²)

⟶ x³ - y³ = x³ + x²y + xy² - x²y - xy² - y³

⟶ x³ - y³ = x³ - y³

For example,

Let us assume that,

x = 1

y = 2

So,

✯ x³ + y³ = 1³ + 2³

⟹ (x + y)(x² - xy + y²) = 1 + 8

⟹ (1 + 2)(1² - (1)(2) + 2²) = 9

⟹ 3 * (1 - 2 + 4) = 9

⟹ 3 * 3 = 9

⟹ 9 = 9

✯ x³ - y³ = 1³ - 2³

⟹ (1 - 2) * (1² + (1)(2) + 2²) = 1 - 8

⟹ ( - 1) * (1 + 2 + 4) = - 7

⟹ ( - 1) * (7) = - 7

⟹ - 7 = - 7

Thus , they can be called as identities/formulae as they are very useful in finding the value of a certain equation or an expression easily.

I hope it will help you.

Regards.