Question

(x2−1)×(x+2)−x2×(x+2)=21    giúp mik vs

Answer 1

\(\left(x^2-1\right).\left(x+2\right)-x^2.\left(x+2\right)=21\\ \Leftrightarrow x^3+2x^2-x-2-x^3-2x^2=21\\ \Leftrightarrow x-2=21\\ \Leftrightarrow x=23\)

Answer 2

\(\left(x^2-1\right).\left(x+2\right)-x^2.\left(x+2\right)=21\)

\(\Leftrightarrow\left(x+2\right).\left(x^2-1-x^2\right)=21\)

\(\Leftrightarrow\left(x+2\right).\left(-1\right)=21\)

\(\Leftrightarrow-x-2=21\)

\(\Leftrightarrow-x=21+2\)

\(\Leftrightarrow-x=23\)

\(\Leftrightarrow x=-23\)

Answer 3

(x2−1).(x+2)−x2.(x+2)=21⇔x3+2x2−x−2−x3−2x2=21⇔x−2=21⇔x=23

Answer 4

$\left({}^{}-1\right).\left(x+2\right)-{}^{}.\left(x+2\right)=21$

$\iff \left(x+2\right).\left({}^{}-1-{}^{}\right)=21$

$\iff \left(x+2\right).\left(-1\right)=21$

$\iff -x-2=21$

$\iff -x=21+2$

$\iff -x=23$

$\iff x=-23$