2（x²+2x）²=3-5（x²+2x）²
2（x²+2x）²+5（x²+2x）²=3
7（x²+2x）²=3
（x²+2x）²=3/7
x²+2x=±√(3/7)=±√21/7
x²+2x+1=1±√21/7
(x+1)²=1±√21/7
x1=-1+√(1+√21/7)
x2=-1-√(1+√21/7)
x3=-1+√(√21/7-1)i
x2=-1-√(√21/7-1)i