n1

1) (a-7)(2b+1)=2ab+a-14b-7

2) (2a-3)(4a-1)=8a²-14a+3

3) (2a-b)(4a²+2ab+b²) = 8a³-b³

n2

(a-3)(a-9)-3a(5-2a) = a²-9a-3a+27-15a+6a²=7a²-27a+27

n3

(x+3)(x-2)-(x+4)(x-3)=6x

x²-2x+3x-6-(x²-3x+4x-12)=6x

x²-2x+3x-6-(x²+x-12)=6x

x²-2x+3x-6-x²-x+12=6x

6=6x

6x=6

x=1