Question

(x+5x)²-4(x²+5x)-12=0

Answer 1

$\displaystyle \tt (x+5x)^2-4(x^2+5x)-12=0\\\displaystyle \tt (6x)^2-4x^2-20x-12=0\\\displaystyle \tt 36x^2-4x^2-20x-12=0\\\displaystyle \tt 32x^2-20x-12=0 \: \: \: \: | \div4\\\displaystyle \tt 8x^2-5x-3=0\\\displaystyle \tt D=(-5)^2-4\cdot8\cdot(-3)=25+96=121\\\displaystyle \tt \sqrt{D}=\sqrt{121}=11\\\displaystyle \tt x_1=\frac{5+11}{2\cdot8}=\frac{16}{16}=1\\\displaystyle \tt x_2=\frac{5-11}{2\cdot8}=\frac{-6}{16}=-\frac{3}{8}=-0,375$