Question

Решите уравнение. 2x^2+x−21=−8x^2

Answer 1

$2x^2+x-21=-8x^2 \\ 2x^2+x-21+8x^2=0 \\ 10x^2+x-21=0 \\ x= \frac{-1+- \sqrt{1^2-4*10(-21)} }{2*10} \\ x= \frac{-1+- \sqrt{1+840} }{20} \\ x= \frac{-1+- \sqrt{841} }{20} \\ x= \frac{-1+-29}{20} \\ \left[\begin{array}{ccc}x= \frac{-1+29}{20} \\ x= \frac{-1-29}{20} \end] \\ \left[\begin{array}{ccc}x= \frac{7}{5} \\ x= -\frac{3}{2} \end]$