Question

Rinu quickly calculated 87square-13square as 7400.explain the method rinu used.use this find 64square-36square

Answer 1

we know that a^2-b^2=(a+b)(a-b)
so 87^2-13^2=(87+13)(87-13)=(100)(74)=7400
the same method is used for the other
64^2-36^2=(64+36)(64-36)=100*28=2800

Answer 2

If you use the identity, then you can easily calculate it.
You are asked to find 87² - 13²
use the identity: a² - b² = (a+b)(a-b)
here a=87, b = 13

87² - 13²
= (87+13)(87-13)
= 100 × 74
= 7400

similarly to calculate 64² - 36²
a=64, b=36
64² - 36² = (64+36)(64-36) = 100 × 28 = 2800