Question

chứng minh

a) (x+y+z)²=x²+y²+z²+2xy+2yz+2xz

Answer 1

\(\left(x+y+z\right)^2\)

\(=\left(x+y\right)^2+2z\cdot\left(x+y\right)+z^2\)

\(=x^2+y^2+z^2+2xy+2xz+2yz\)

Answer 2

Ta có:

\(\left(x+y+z\right)^2=\left(x+y\right)^2+z^2+2\left(x+y\right)z\)

\(=x^2+y^2+2xy+z^2+2xz+2yz\)

\(=x^2+y^2+z^2+2xy+2xz+2yz\) (đpcm)