Toán Lớp 8: Viết các biểu thức sau dưới dạng đa thức: a) (2a-b)(b+4a)+2a(b-3a) b) (3a-2b)(2a-3b)-6a(a-b) c) 5b(2x-b)-(8b-x)(2x-b) d) 2x(a+15x)+(x-6

Question

Toán Lớp 8:  Viết các biểu thức sau dưới dạng đa thức: a) (2a-b)(b+4a)+2a(b-3a) b) (3a-2b)(2a-3b)-6a(a-b) c) 5b(2x-b)-(8b-x)(2x-b) d) 2x(a+15x)+(x-6a)(5a+2x)

mocmien87 · Answer

Giải đáp:   a)2a&sup2;-b&sup2;   b)6b&sup2;-7ab   c)2x&sup2;-7bx+3b&sup2;   d)-5ax+32x&sup2;-30a&sup2;   Lời giải và giải thích chi tiết:   a)(2a-b)(b+4a)+2a(b-3a)   =2ab+8a&sup2;-b&sup2;-4ab+2ab-6a&sup2;   =(2ab-4ab+2ab)+(8a&sup2;-6a&sup2;)-b&sup2;   =2a&sup2;-b&sup2;   b)(3a-2b)(2a-3b)-6a(a-b)   =6a&sup2;-9ab-4ab+6b&sup2;-6a&sup2;+6ab   =(6a&sup2;-6a&sup2;)+6b&sup2;+(-9ab-4ab+6ab)   =6b&sup2;-7ab   c)5b(2x-b)-(8b-x)(2x-b)   =10bx-5b&sup2;-(16bx-8b&sup2;-2x&sup2;+bx)   =10bx-5b&sup2;-16bx+8b&sup2;+2x&sup2;-bx   =2x&sup2;+(10bx-16bx-bx)+(-5b&sup2;+8b&sup2;)   =2x&sup2;-7bx+3b&sup2;   d)2x(a+15x)+(x-6a)(5a+2x)   =2ax+30x&sup2;+5ax+2x&sup2;-30a&sup2;-12ax   =(2ax+5ax-12ax)+(30x&sup2;+2x&sup2;)-30a&sup2;   =-5ax+32x&sup2;-30a&sup2;

maingoctruc · Answer

#AkaShi   (2a-b)(b+4a)+2a(b-3a)   =2ab+8a^2-b^2-4ab+2ab-6a^2   =(2ab-4ab+2ab)+(8a^2-6a^2)-b^2   =2a^2-b^2   ...................   (3a-2b)(2a-3b)-6a(a-b)   =6a^2-9ab-4ab+6b^2-6a^2+6ab   =(6a&sup2;-6a&sup2;)+(-9ab-4ab+6ab)+6b^2   =-7ab+6b&sup2;   ..................   5b(2x-b)-(8b-x)(2x-b)   =10bx-5b&sup2;-(16bx-8b&sup2;-2x&sup2;+bx)   =10bx-5b&sup2;-16bx+8b&sup2;+2x&sup2;-bx   =(-5b&sup2;+8b&sup2;)+(10bx-16bx-bx)+2x&sup2;   =3b&sup2;+2x&sup2;-7bx   .................   2x(a+15x)+(x-6a)(5a+2x)   =2ax+30x&sup2;+5ax+2x&sup2;-30a&sup2;-12ax   =(2ax+5ax-12ax)+(30x&sup2;+2x&sup2;)-30a&sup2;   =-5ax+32x&sup2;-30a&sup2;