Question

(a+b) . (m+n) =a.m +a.n+b.m +b.n

Tính

a) (x-3) (x+7)

b) (2x-5) ( x-1)

Answer 1

\(\)Ta có:

\(VT=\left(a+b\right)\left(m+n\right)=am+an+bm+bn\)

\(=VP\rightarrowđpcm\)

Ta có:

\(\left(x-3\right)\left(x+7\right)=x^2+7x-3x-21\)

\(=x^2-4x-21\)

\(\left(2x-5\right)\left(x-1\right)\)

\(=2x^2-2x-5x+5\)

\(=2x^2-7x+5\)

Answer 2

a, \(\left(x-3\right)\left(x+7\right)=x^2+7x-3x-21=x^2+4x-21\)

b, \(\left(2x-5\right)\left(x-1\right)=2x^2-2x-5x+5=2x^2-7x+5\)