Question

Answer 1

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

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

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

\(\Leftrightarrow2b.2a=4ab\left(đúng\right)\)

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

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

\(\Leftrightarrow\left(a-b-a-b\right)\left(a-b+a+b\right)=-45ab\)

\(\Leftrightarrow-2b.2a=-4ab\left(đúng\right)\)

Answer 2

Ta có:

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

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