Question

1. Tìm x biết:

1. (2-x)^2-9=0

2. (X-3)^3 - (x-3)×(x^2+3x+9)= 15-9(x+1)^2

Mọi người giúp em với ạ, em cảm ơn.

Answer 1

\(1,\left(2-x\right)^2-9=0\)

\(\Leftrightarrow\left(2-x-9\right)\left(2-x+9\right)=0\)

\(\Leftrightarrow\left(-7-x\right)\left(11-x\right)=0\)

\(\Rightarrow\left[{}\begin{matrix}-7-x=0\\11-x=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=-7\\x=11\end{matrix}\right.\)

\(b,\left(x-3\right)^3-\left(x-3\right)\left(x^2+3x+9\right)=15-9\left(x+1\right)^2\)\(\Leftrightarrow x^3-9x^2+27x-27-x^3-27=15-9x^2-18x-9\)\(\Leftrightarrow x^3-9x^2+27x-x^3+9x^2+18x=15+27+27\)\(\Leftrightarrow45x=69\Rightarrow x=\dfrac{23}{15}\)

Answer 2

1. \(\left(2-x\right)^2-9=0\)

\(\left(2-x\right)^2=9\)

\(\left(2-x\right)^2=3^2\)

\(2-x=3\)

\(-x=-1\Rightarrow x=1\)