`1. `

`a)x^2y-7x^2y+5xy^2 `

`=-6x^2y+5xy^2 `

`b)-5xy^3-7y^2xy `

`=-5xy^3-7y^3x `

`=-12xy^3 `

`c)3x^4-(5x^2)^2 `

`=3x^4-25x^4 `

`=-22x^4 `

`d)2xy^2  .(-1/3x^2y^3)^2 `

`=2xy^2  .  1/9x^4y^5 `

`=2/9x^5y^7 `

`e)x^2(x-1)-(x^2+1)(x+2) `

`=x^3-x^2-(x^3+2x^2+x+2) `

`=x^3-x^2-x^3-2x^2-x-2 `

`=-3x^2-x-2 `

`f)(x-5)(x^2+26)+(5-x)(1-5x) `

`=(x-5)(x^2+26)-(x-5)(1-5x) `

`=(x-5)(x^2+26-1+5x) `

`=(x-5)(x^2+5x+25) `

`=x^3-5^3 `

`=x^3-125 `

`g)(3x-5)(2x+11)-(2x+3)(3x+7) `

`=6x^2+33x-10x-55-(6x^2+14x+9x+21) `

`=6x^2+33x-10x-55-6x^2-14x-9x-21 `

`=-76 `

`h)(3x^2y^2+6x^2y^3-12xy):3xy `

`=xy+2xy^2-4 `