Question

[Lê Thị Phương Linh]

Giải giúp mình với ạ. Mình cảm ơn

Answer 1

[Lấp La Lấp Lánh]

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

\(\Leftrightarrow\dfrac{a^2+2ab+b^2-a^2+2ab-b^2}{4}=ab\)

\(\Leftrightarrow\dfrac{4ab}{4}=ab\left(đúng\right)\)

b) \(2\left(x^2+y^2\right)=\left(x+y\right)^2+\left(x-y\right)^2\)

\(\Leftrightarrow2x^2+2y^2=x^2+2xy+y^2+x^2-2xy+y^2\)

\(\Leftrightarrow2x^2+2y^2=2x^2+2y^2\left(đúng\right)\)

c) \(\left(x+y\right)^2-\left(x-y\right)\left(x+y\right)=2y\left(x+y\right)\)

\(\Leftrightarrow\left(x+y\right)\left(x+y-x+y\right)=2y\left(x+y\right)\)

\(\Leftrightarrow\left(x+y\right).2y=2y\left(x+y\right)\left(đúng\right)\)