Đáp án:
`a)28x^4-12x³+62x²-18x+30`
`b)-4x³+14x²-10x+2`
`c)ax^4-4ax³+2ax²+bx³-4bx²+2bx+cx²-4cx+2c`
Giải thích các bước giải:
`a)(-3x+5+7x²)(4x²+6)`
`=-12x³-18x+20x²+30+28x^4+42x²`
`=28x^4-12x³+(20x²+42x²)-18x+30`
`=28x^4-12x³+62x²-18x+30`
`b)(x²-3x+1)(2-4x)`
`=2x²-4x³-6x+12x²+2-4x`
`=-4x³+(2x²+12x²)-(6x+4x)+2`
`=-4x³+14x²-10x+2`
`c)(ax²+bx+c)(2-4x+x²)`
`=2ax²-4ax³+ax^4+2bx-4bx²+bx³+2c-4cx+cx²`
`=ax^4-4ax³+bx³+2ax²-4bx²+cx²+2bx-4cx+2c`