Question

докажи тождество (a+b)^2-(a-b)^2=4ab

Answer 1

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