A2+a4=14 a7=a3+12 a1=? d=?
a1+d+a1+3d=14 a1+2d=7 a1=7-2d
a7=7+12=19 a1+6d=19 7-2d+6d=19 4d=12 d=3 a1=7-6=1
<span> (4x-3y)(x+2y)+2x(x+2y)=(4x-3y+2x)(x+2y)=3(2x-y)(x+2y)
5a(3a-b)+(b-3a)(5а+2b);= (b-3a)(-5a+5a+2b)=2b(b-3a)
(a+b)(x-y)+(b-a)(y-x);= (x-y)(a+b-b+a)=2a(x-y)
(2a+7b)(a-5b)-(8b-3a)(a-5b)= (a-5b)(2a+7b-8b+3a)=(a-5b)(5a-b)</span>