Tìm x biết \(2\left(2x-5\right)^2-\left(2x-3\right)^2-\left(2x-1\right)\left(2x+1\right)=70\)
Hướng dẫn giải
Ta có:\(2\left(2x-5\right)^2-\left(2x-3\right)^2-\left(2x-1\right)\left(2x+1\right)=70\)
\(\Leftrightarrow2\left(4x^2-20x+25\right)-\left(4x^2-12x+9\right)-\left(4x^2-1\right)=70\)
\(\Leftrightarrow8x^2-40x+50-4x^2+12x-9-4x^2+1=70\)
\(\Leftrightarrow-28x+42=70\Leftrightarrow-28x=28\Leftrightarrow x=-1.\)