Đáp án:
`12)33/20x²+1/2x`
`13)-5/6x²y^5-xy`
Giải thích các bước giải:
`12)1/4x²-(5/2x-7/5x²-1)+(5/2x-1+1/2x)`
`=1/4x²-5/2x+7/5x²+1+5/2x-1+1/2x`
`=(1/4x²+7/5x²)+(-5/2x+5/2x+1/2x)+(1-1)`
`=(5/20x²+28/20x²)+1/2x`
`=33/20x²+1/2x`
`13)5/3x²y^5-(1/2x³y^4-3/2xy+5/2x²y^5)+(1/2x³y^4-1/2xy)`
`=5/3x²y^5-1/2x³y^4+3/2xy-5/2x²y^5+1/2x³y^4-1/2xy`
`=(5/3x²y^5-5/2x²y^5)+(-1/2x³y^4+1/2x³y^4)+(3/2xy-1/2xy)`
`=(10/6x²y^5-15/6x²y^5)-2/2xy`
`=-5/6x²y^5-xy`
