若x1满足2x+2^x=5,x2满足2x+2log2(x-1)=5,则x1+x2=?
若x1满足2x+2^x=5,x2满足2x+2log2(x-1)=5,则x1+x2=?
日期:2016-12-02 04:27:34 人气:2
答:
x1满足:2x+2^x=5,2x1+2^(x1)=5
x2满足:2x+2log2(x-1)=5,2x2+2log2(x2-1)=5
设t=log2(x2-1)
则x2-1=2^t
所以:x2=1+2^t
所以:2(1+2^t)+2t=5
所以:2(t+1)+2^(t+1)=5
所以:
x1和t+1都是方程2x+2^x=5的解
所以:x1=t+1=log2(x2-1)+1=log2(2x2-2)
2x2-2=2^(x1)
2x2=2+2^(x1)
所以:
2x1+2x2=2