Toán Lớp 8: A=2y(x+y)+3x(x-y)+15 B=(7x+5)^2+(3x-5)^2-(10-6x)(5+7x) C=(2x+y)(y^2+4x^2-2xy)-8x(x-1)(x-1)

Question

Toán Lớp 8:  A=2y(x+y)+3x(x-y)+15 B=(7x+5)^2+(3x-5)^2-(10-6x)(5+7x) C=(2x+y)(y^2+4x^2-2xy)-8x(x-1)(x-1)

quynhmaithu · Answer

$A=2y(x+y)+3x(x-y)+15$   $=2xy+2y^2+3x^2-3xy+15$   $=3x^2+2y^2-xy+15$   $B=(7x+5)^2+(3x-5)^2-(10-6x)(5+7x)$   $=49x^2+70x+25+9x^2-30x+25-(70x+50-30x-42x^2)$   $=49x^2+9x^2+42x^2+70x-30x-70x+30x-50+25+25$   $=100x^2$   $C=(2x+y)(y^2+4x^2-2xy)-8x(x-1)(x-1)$   $=(2x+y)(4x^2-2xy+y^2)-8x(x^2-2x+1)$   $=8x^3+y^3-8x^3+16x^2-8x$   $=y^3+16x^2-8x$

tonhitruc · Answer

Giải đáp:   A=3x&sup2;+2y&sup2;-xy+15   B=100x&sup2;   C=y&sup3;+16x&sup2;-8x   Lời giải và giải thích chi tiết:   A=2y(x+y)+3x(x-y)+15   =2xy+2y&sup2;+3x&sup2;-3xy+15   =3x&sup2;+2y&sup2;+(2xy-3xy)+15   =3x&sup2;+2y&sup2;-xy+15   B=(7x+5)&sup2;+(3x-5)&sup2;-(10-6x)(5+7x)   =(7x+5)&sup2;-(10-6x)(5+7x)+(3x-5)&sup2;   =(7x+5)&sup2;+(6x-10)(7x+5)+(3x-5)&sup2;   =(7x+5)&sup2;+2.(7x+5).(3x-5)+(3x-5)&sup2;   =(7x+5+3x-5)&sup2;   =(10x)&sup2;   =100x&sup2;   C=(2x+y)(y&sup2;+4x&sup2;-2xy)-8x(x-1)(x-1)   =(2x+y)(4x&sup2;-2xy+y&sup2;)-8x(x-1)&sup2;   =(2x+y)[(2x)&sup2;-2x.y+y&sup2;]-8x(x&sup2;-2x+1)   =(2x)&sup3;+y&sup3;-8x&sup3;+16x&sup2;-8x   =8x&sup3;+y&sup3;-8x&sup3;+16x&sup2;-8x   =(8x&sup3;-8x&sup3;)+y&sup3;+16x&sup2;-8x   =y&sup3;+16x&sup2;-8x