Question

mọi người ơi giúp tớ bài này với ạ

Answer 1

Ta có: `3m-2n=5`

`<=>9m^2-12mn+4n^2=25`

`<=>9m^2+12mn+4n^2-24mn=25`

`<=>(3m+2n)^2-24.(-1)=25`

`<=>(3m+2n)^2=1`

`<=>|3m+2n|=1`

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`a)A=n(m-2)+3m`

`<=>A=mn-2n+3m`

`<=>A=3m-2n+mn`

`<=>A=5-1=4`

~~~~~~~~~~~~~~~~~~~~

`b)B=9m^2+4n^2`

`<=>B=(3m+2n)^2-12mn`

`<=>B=1-12.(-1)=13`

~~~~~~~~~~~~~~~~~~~

`c)C=81m^4+16n^4`

`<=>C=(9m^2-4n^2)^2+72m^2 n^2`

`<=>C=[(3m-2n)(3m+2n)]^2+72(mn)^2`

`<=>C=(3m-2n)^2(3m+2n)^2+72(mn)^2`

`<=>C=5^2 .1^2+72.(-1)^2`

`<=>C=25+72=97`

~~~~~~~~~~~~~~~~~~~~~~

`d)D=|3m+2n|=1`

~~~~~~~~~~~~~~~~~~~~~

`e)E=(10+3m)^2-4n(10+3m)+4n^2`

`<=>E=(10+3m-2n)^2`

`<=>E=(10+5)^2=15^2=225`