根号(5x方+10x+1)+x方+2x=7
根号[5(x²+2x)+1]=7-(x²+2x)
令x²+2x=u
根号[5u+1]=7-u
两边平方:
5u+1=49-14u+u²
u²-19u+48=0
(u-16)(u-3)=0
u-16=0,u1=16;x²+2x-16=0,x=[-2±√(2²+4*16)]/2,x1=-1+√17;x2=-1-√17;
u2=3;x²+2x-3=0,(x+3)(x-1)=0,x3=-3,x4=1;
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