Thu gọn biểu thức:
\(9x\left(x+5\right)-\left(3x+2\right)\left(3x-2\right)\)
\(=9x^2+45x-\left(9x^2-4\right)\)
\(=45x+4\)
Tìm x. biết:
\(\left(3x-2\right)^2=49x^2\)
\(\Leftrightarrow\left[{}\begin{matrix}3x-2=7x\\3x-2=-7x\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}x=-\dfrac{1}{2}\\x=\dfrac{1}{5}\end{matrix}\right.\)
Vậy \(x\in\left\{-\dfrac{1}{2};\dfrac{1}{5}\right\}\)
a: Ta có: \(9x\cdot\left(x+5\right)-\left(3x+2\right)\left(3x-2\right)\)
\(=9x^2+45x-9x^2+4\)
=45x+4
b: Ta có: \(\left(3x-2\right)^2=49x^2\)
\(\Leftrightarrow\left(3x-2-7x\right)\left(3x-2+7x\right)=0\)
\(\Leftrightarrow\left(4x+2\right)\left(10x-2\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=-\dfrac{1}{2}\\x=\dfrac{1}{5}\end{matrix}\right.\)
