Question

chứng minh công thức : (x-y)^2=(x+y) ^2-4xy

Answer 1

\(\begin{array}{l} \text{Xét:}\\ VP=(x+y)^2-4xy\\ =x^2+2xy+y^2-4xy\\ =x^2+(2xy-4xy)+y^2\\ =x^2-2xy+y^2\\ =(x-y)^2=VT\ \text{(đpcm)}\end{array}\)

Answer 2

Ta có: \(\left(x+y\right)^2-4xy\)

\(=x^2+2xy+y^2-4xy\)

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

\(=\left(x-y\right)^2\)(đpcm)