若x1满足2x+2x=5,x2满足2x+2log2(x-1)=5,x1+x2=( ) A.52 B.3 C.72 D.4
问题描述:
若x1满足2x+2x=5,x2满足2x+2log2(x-1)=5,x1+x2=( )
A.
5 2
B. 3
C.
7 2
D. 4
答
由题意2x1+2x1=5①2x2+2log2(x2-1)=5 ②所以2x1=5−2x1,x1=log2(5-2x1) 即2x1=2log2(5-2x1)令2x1=7-2t,代入上式得7-2t=2log2(2t-2)=2+2log2(t-1)∴5-2t=2log2(t-1)与②式比较得t=...