Question

Find the cube of 75 using (a+b) power 3 and check your result using (a_b)power3

Answer 1

Let 75 be (70+5)

(a+b)^3= a^3 + b^3 +3a^2b +3ab^2

(70+5)^3=(70)^3 + (5)^3 + 3(70)^2 (5) + 3(70)(5)^2

= 343000 + 125 + 73500 + 5250

=421875

verification...

let it be 80-5

(80-5)^3 = 80^3 -5^3 - 3*80^2*5 + 3*80*5^2

= 512000-125-96000+126000

=421875

HENCE PROVED