Question

解方程（2X+1）4 - 8(2X+1)2+15=0

Answer 1

令(2x+1)²=a

则a²-8a+15=0

(a-3)(a-5)=0

a=3,a=5

(2x+1)²=3

2x+1=±√3

x=(-1±√3)/2

(2x+1)²=5

2x+1=±√5

x=(-1±√5)/2

所以

x1=(-1+√3)/2

x2=(-1-√3)/2

x3=(-1+√5)/2

x4=(-1-√5)/2