第1个回答 2010-04-16
3.√2-1=1/(√2+1)=(√2+1)^(-1),原方程化为
(√2+1)^x+(√2+1)^(-x)=6,
两边都乘以(√2+1)^x,得
(√2+1)^2x-6(√2+1)^x+1=0.
解得(√2+1)^x=3±2√2,
即(√2+1)^x=(√2±1)²,
所以x=2,或x=-2.
4.方程组化为 8*2^x+9*9^y=35,
2^x+ 3*9^y =5.
令2^x=m,9^y=n,则
8m+9n=35,m+3n=5.
解得m=4,n=1/3.
即2^x=4,9^y=1/3,
则x=2,y=-1/2.
5.化为2log(2)x-3/【log(2)x】-5=0,
得2log(2)²x-5log(2)x-3=0.
【2log(2)x-3】【log(2)x+1】=0.
则 log(2)x=3/2,或log(2)x=-1.
所以x=2^(3/2),或 x=1/2.
6.有空再作.