1.(lg2)^3+(lg5)^3+3lg2*lg5=
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1.(lg2)^3+(lg5)^3+3lg2*lg5=
2.若lg(x-y)+lg(x+2y)=lg2+lgx+lgy,则x/y=
2.若lg(x-y)+lg(x+2y)=lg2+lgx+lgy,则x/y=
![1.(lg2)^3+(lg5)^3+3lg2*lg5=](/uploads/image/z/9756533-29-3.jpg?t=1.%EF%BC%88lg2%EF%BC%89%5E3%2B%28lg5%29%5E3%2B3lg2%2Alg5%3D)
1.设x=lg2,y=lg5,则x+y=lg2+lg5=lg10=1
原式=x^3+y^3+3xy
=(x+y)(x^2-xy+y^2)+3xy
=x^2-xy+y^2+3xy
=x^2+2xy+y^2
=(x+y)^2
=1
2.
lg(x-y)+lg(x+2y)=lg2+lgx+lgy
lg(x-y)(x+2y)=lg2xy
(x-y)(x+2y)=2xy
x^2+xy-2y^2=2xy
x^2-xy-2y^2=0
设x/y=k
k^2y^2-ky^2-2y^2=0
(k^2-k-2)Y^2=0
k^2-k-2=0
(k+1)(k-2)=0
k=-1,k=2
x/y=-1(舍),x/y=2
原式=x^3+y^3+3xy
=(x+y)(x^2-xy+y^2)+3xy
=x^2-xy+y^2+3xy
=x^2+2xy+y^2
=(x+y)^2
=1
2.
lg(x-y)+lg(x+2y)=lg2+lgx+lgy
lg(x-y)(x+2y)=lg2xy
(x-y)(x+2y)=2xy
x^2+xy-2y^2=2xy
x^2-xy-2y^2=0
设x/y=k
k^2y^2-ky^2-2y^2=0
(k^2-k-2)Y^2=0
k^2-k-2=0
(k+1)(k-2)=0
k=-1,k=2
x/y=-1(舍),x/y=2
1.(lg2)^3+(lg5)^3+3lg2*lg5=
lg2(lg5-lg2)-lg5(lg5+3lg2)等于
(lg2)^3+(lg5)^3+3*lg2*lg5
(lg2)³+(lg5)³+3lg2×lg5
(lg2)^3+(lg5)^3+3lg2*lg5等于?
(lg2)³+(lg5)³+3lg2×lg5=?
(lg2)^3+(lg5)^2=
3+lg5+(lg2)^2
(lg2)^3+(lg5)^3+lg5*lg8
对数运算题(lg2)^3+3lg2*lg5+(lg5)^3=多少
lg2^2+lg2*lg5+lg5=lg2(lg2+lg5)+lg5
(lg2)^3+(lg5)^3+3lg2*lg5 这些怎么算.