Question

Решить уравнение 3/4х+(85-х)*5/9=55

Answer 1

$frac{3}{4x}+frac{(85-x)*5}{9}=55|*(9*4x)\3*5+(85-x)*5*4x=55*36x\15+(85-x)*20x=1980x\15+1700x-20x^2=1980x\-20x^2-280x+15=0|*(-1)\20x^2+280x-15=0|:5$

$4x^2+56x-3=0\D^2=56^2-4*4*(-3)=3136+16*3=3136+48=3184\D=sqrt{3184}=+-4sqrt{199}\x_1=frac{-56+4sqrt{199}}{2*4}=frac{4(-14+sqrt{199})}{8}=frac{-14+sqrt{199}}{2}=-7+frac{sqrt{199}}{2}\x_1=-7-frac{sqrt{199}}{2}$