4*4^x-5*2^x-6=0,求x的值 9^x+6^x=2^(2x+1) 求x值
两题啊
人气:144 ℃ 时间:2019-10-17 06:52:43
解答
1.
设t=2^x
由于:4*4^x-5*2^x-6=0
则:4*(2^x)^2-5*2^x-6=0
即:4t^2-5t-6=0
则有:(t-2)(4t+3)=0
由于:t=2^x>0恒成立
故:4t+3>0
则:t-2=0
即:2^x=2
故:x=1
2.设X=3^x,Y=2^x
由于:9^x+6^x=2^(2x+1)
则:(3^x)^2+(2^x)*(3^x)-2(2^x)^2=0
即:X^2+XY-2Y^2=0
则:(X-Y)(X+2Y)=0
由于:X=3^x>0,Y=2^x>0
则:X+2Y>0
则:X-Y=0
即:3^x=2^x
故:x=0
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