x(2x2+7)=7x2+2
2x³+7x=7x²+2
2x³+7x-7x²-2=0
2x³-7x²+7x-2=0
2(x³-1)-7x(x-1)=0
2(x-1)(x²+x+1)-7x(x-1)=0
(x-1)[2(x²+x+1)-7x]=0
(x-1)(2x²+2x+2-7x)=0
(x-1)(2x²-5x+2)=0
x-1=0 ∨ 2x²-5x+2=0
x=1 Δ= 25-4*2*2=25-16=9
√Δ=3
x₁=(5-3):4=½
x₂=(5+3):4=2
odp. x∈{½; 1; 2