Question

(x+5x)²-4(x²+5x)-12=0

Answer 1

$displaystyle tt (x+5x)^2-4(x^2+5x)-12=0\displaystyle tt (6x)^2-4x^2-20x-12=0\displaystyle tt 36x^2-4x^2-20x-12=0\displaystyle tt 32x^2-20x-12=0 : : : : | div4\displaystyle tt 8x^2-5x-3=0\displaystyle tt D=(-5)^2-4cdot8cdot(-3)=25+96=121\displaystyle tt sqrt{D}=sqrt{121}=11\displaystyle tt x_1=frac{5+11}{2cdot8}=frac{16}{16}=1\displaystyle tt x_2=frac{5-11}{2cdot8}=frac{-6}{16}=-frac{3}{8}=-0,375$