Question

rút gọn A=(x+a)(x+b)(x+c) biết a+b=c=6; ab+bc+ca=-7; abc=-60

Answer 1

không biết làm hâhha

Answer 2

\(A=\left(x^2+\left(a+b\right)x+ab\right)\left(x+c\right)=x^3+\left(a+b+c\right)x^2+\left(ab+bc+ac\right)x+abc\)

\(A=x^3+6x^2-7x-60\)

Nếu rút gọn thành nhân tử thì:

\(A=x^3-3x^2+9x^2-27x+20x-60=x^2\left(x-3\right)+9x\left(x-3\right)+20\left(x-3\right)\)

\(=\left(x-3\right)\left(x^2+9x+20\right)=\left(x-3\right)\left(x^2+4x+5x+20\right)=\left(x-3\right)\left[x\left(x+4\right)+5\left(x+4\right)\right]\)

\(A=\left(x-3\right)\left(x+4\right)\left(x+5\right)\).