问题：3的x次方=4,3的y次方=6,求9的2x-y次方+27x-y次方的值.答案：9^2x-y+27^x-y=3^4x-2y+3^3x-3y=3^4x/3^2y+3^3x/3^3y=(3^x)^4/(3^y)^2+(3^x)^3/(3^y)^3=4^4/6^2+4^3/6^3=256/36+64/216=64/9+8/27=192/27+8/27=200/27我想知道3^4x-2

Question

问题：3的x次方=4,3的y次方=6,求9的2x-y次方+27x-y次方的值.
答案：9^2x-y+27^x-y
=3^4x-2y+3^3x-3y
=3^4x/3^2y+3^3x/3^3y
=(3^x)^4/(3^y)^2+(3^x)^3/(3^y)^3
=4^4/6^2+4^3/6^3
=256/36+64/216
=64/9+8/27
=192/27+8/27
=200/27
我想知道3^4x-2y+3^3x-3y这一步怎么来的?

Answer 1

9^2(x-y)+27^(x-y)
小括号也不打!
9=3^2
(3^[2*2(x-y)]=3^(4x-2y)
27=3^3
(3^[3*(x-y)]=3^(3x-3y)
3^4x-2y+3^3x-3y