Question

Thực hiện phép tính

a) (m+n)² -(m-n)² +(m+n)(m-n)

b)(x-1)³+3(x-2)(x+1)-(x²+x+1)(x-1)

Answer 1

a,\(\left(m+n\right)^2\left(m-n\right)^2+\left(m+n\right)\left(m-n\right)\)

\(\Leftrightarrow2n.2m+m^2-n^2\)

\(\Leftrightarrow4mn+m^2-n^2\)

b,\(\left(x-1\right)^3+3\left(x-2\right)\left(x+1\right)-\left(x^2+x+1\right)\left(x-1\right)\)

\(\Leftrightarrow x^3-3x^2+3x-1+\left(3x-6\right)\left(x+1\right)-\left(x^3-1\right)\)

\(\Leftrightarrow x^3-3x^2+3x-1+3x^2+3x-6x-6-x^3+1\)

\(\Leftrightarrow-6\)