9^x+4^x=2.5*6^x

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9^x+4^x=2.5*6^x
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9^x+4^x=2.5*6^x
9^x+4^x=2.5*6^x

9^x+4^x=2.5*6^x
两边同时除以6^x,则
(4/6)^x+(6/6)^x>(9/6)^x
(2/3)^x+1>(3/2)^x,
令(2/3)^x=y 且 y>0
y+1>1/y
y^2+y-1>0
因为y>0,解得y>[5^(1/2)-1]/2 ,(根号5不会表示)
接下去,自己做吧

a = 2^x, b = 3^x
a^2 + b^2 - 2.5ab = 0
a= 2b 或 b = 2a
(2/3)^x = 2 或 (3/2)^x = 2
可求解
x = log(2/3) 2 或 x = log(3/2) 2