\(\left(x+3\right)^2-x\left(x-5\right)=31\)
\(\Leftrightarrow x^2+6x+9-x^2+5x=31\)
\(\Leftrightarrow11x=22\)
\(\Leftrightarrow x=2\)
\(\left(4x+3\right)\left(x-2\right)-\left(2x-1\right)^2=50\)
\(\Leftrightarrow4x^2-8x+3x-6-4x^2+4x-1=50\)
\(\Leftrightarrow-x=56\Leftrightarrow x=-56\)
\(\left(3x+5\right)\left(3x-5\right)-9x\left(x+20\right)=18\)
\(\Leftrightarrow9x^2-25-9x^2-180x=18\)
\(\Leftrightarrow-180x=43\)
\(\Leftrightarrow x=-\dfrac{43}{180}\)
a ) \(\left(x+3\right)^2-x\left(x-5\right)=31\)
\(\Leftrightarrow x^2+6x+9-x^2+5x=31\)
\(\Leftrightarrow11x+9=31\)
\(\Leftrightarrow11x=22\)
\(\Leftrightarrow x=2\)
Vậy \(x=2\)
b ) \(\left(4x+3\right)\left(x-2\right)-\left(2x-1\right)^2=50\)
\(\Leftrightarrow4x^2+3x-8x-6-\left(4x^2-4x+1\right)=50\)
\(\Leftrightarrow4x^2-5x-6-4x^2+4x-1=50\)
\(\Leftrightarrow\left(4x^2-4x^2\right)-\left(5x-4x\right)-\left(6+1\right)=50\)
\(\Leftrightarrow-x-7=50\)
\(\Leftrightarrow-x=57\)
\(\Leftrightarrow x=-57\)
Vậy \(x=-57\)
c ) \(\left(3x+5\right)\left(3x-5\right)-9x\left(x+20\right)=18\)
\(\Leftrightarrow9x^2-25-9x^2-180x=18\)
\(\Leftrightarrow-25-180x=18\)
\(\Leftrightarrow180x=-43\)
\(\Leftrightarrow x=-\dfrac{43}{180}\)
Vậy \(x=-\dfrac{43}{180}\)
