Đáp án:
`25)(a-b)(a-9b)`
`28)(9a-b)(5a+b)`
`31)(4a-b)(-2a-3b)`
`33)4(a+2b)(3a+b)`
`35)(5a-b)(a+7b)`
`37)(7x-22)(3x-8)`
Giải thích các bước giải:
`25)(a-5b)²-16b²`
`=(a-5b)²-(4b)²`
`=(a-5b+4b)(a-5b-4b)`
`=(a-b)(a-9b)`
`28)49a²-(2a-b)²`
`=(7a)²-(2a-b)²`
`=[7a+(2a-b)][7a-(2a-b)]`
`=(7a+2a-b)(7a-2a+b)`
`=(9a-b)(5a+b)`
`31)(a-2b)²-(3a+b)²`
`=[(a-2b)+(3a+b)][(a-2b)-(3a+b)]`
`=(a-2b+3a+b)(a-2b-3a-b)`
`=(4a-b)(-2a-3b)`
`33)(4a+3b)²-(b-2a)²`
`=[(4a+3b)+(b-2a)][(4a+3b)-(b-2a)]`
`=(4a+3b+b-2a)(4a+3b-b+2a)`
`=(2a+4b)(6a+2b)`
`=4(a+2b)(3a+b)`
`35)9(a+b)²-4(a-2b)²`
`=[3(a+b)]²-[2(a-2b)]²`
`=[3(a+b)+2(a-2b)][3(a+b)-2(a-2b)]`
`=(3a+3b+2a-4b)(3a+3b-2a+4b)`
`=(5a-b)(a+7b)`
`37)25(x-3)²-(2x-7)²`
`=[5(x-3)]²-(2x-7)²`
`=[5(x-3)+(2x-7)][5(x-3)-(2x-7)]`
`=(5x-15+2x-7)(5x-15-2x+7)`
`=(7x-22)(3x-8)`
Hướng dẫn:
Áp dụng HĐT:`A²-B²=(A+B)(A-B)`
