Question

tính:

a) (x^2 + x +1)(x^2 - x - 1)

b) (a + b)^2 - (a - b)^2

Answer 1

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

\(=x^2-\left(x+1\right)^2\)

\(=x^2-x^2-2x-1\)

\(=-2x-1\)

b, \(\left(a+b\right)^2-\left(a-b\right)^2\)

\(=\left(a+b-a+b\right)\left(a+b+a-b\right)\)

\(=2b.2a=4ab\)

Answer 2

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