Question

Chứng minh :

\(\left(a+b\right)^2-\left(a-b\right)^2=4ab\)

Answer 1

(a+b)^2-(a-b)^2=4ab

a^2+2ab+b^2-a^2+2ab-b^2=4ab

a^2+2ab+b^2-a^2+2ab-b^2-4ab=0

a^2-a^2+2ab+2ab-4ab+b^2-b^2=0

0=0

=>dpcm

Answer 2

Biến đổi vế trái ta có:

\(\left(a+b\right)^2-\left(a-b\right)^2=a^2+2ab+b^2-a^2+2ab-b^2=4ab=VP\)

=>đpcm