解析 2W =5x2-4xv+y2-2y+8x+3=4.x2-4xy+y2+4x-2y+1+x2+4x+4-2=(2 x-y) 2(2r-y)+1+(x+2)-2=(2x-y+1)2+(x+2)-2 因为 r,y为实数,所以(2r-y+1)2≥0.(r+2)2≥0.则 W -2.所以 W的最小值为 -2.故答案为 -2 ...
答案见上-2 解析:本题考查了配方法的应用、非负数的性质. W=5x^2-4xy+y^2- 2y+8x+3=4x2-4xy+y2+4x-2y+1+x2+4x+4-2=(2x-y)2+2(2x-y)+1+ (x+2)^2-2=(2x-y+1)^2+(x+2)^2-2 ,∵x、y 为实数, (2x-y+1)^2≥0 , (x+2)^2≥0 ,..W的最小值为-2,故答...
W = 5x^2-4xy+y^2-2y+8x+3W'x = 10x - 4y + 8, W'y = -4x + 2y - 2, 解得唯一驻点 （-2，-3）A = W''xx = 10 > 0, B = W'xy = -4, C = W'yy = 2, B^2-AC = -4极小值即最小项是 W(-2, -3) = 29 - 24 + 9 + 6 - 16 + 3...
(3)原式=4a2-2a-6-4a2+4a+10=2a+4; (4)原式=2x-3x+ x 2 - 1 2 +5x- 3 2 x+3=3x+ 5 2 ; (5)原式=12x2-9x+6-2+8x2-2x=20x2-11x+4; (6)A-2B=3x2-2xy+y2-2(5x2-4xy-2y2)=x2-2xy+y2-10x2+8xy+4y2=-7x2+6xy+5y2. ...
解答 解:(1)3ax-3ay+xy-y2;=(3ax-3ay)+(xy-y2)=3a(x-y)+y(x-y)=(x-y)(3a+y);(2)8x3+4x2-2x-1=(8x3+4x2)-(2x+1)=4x2(2x+1)-(2x+1)=(2x+1)(4x2-1)=(2x+1)(2x+1)(2x-1)=(2x+1)2(2x-1);(3)5x2-15x+2xy-6y=(5x2-15x)+(2xy-6y)=5x(x-3)+2y(x-3)=...
解析 7本题考查了配方法的应用,非负数的性质. W=5x^2-4xy+y^2- 2y+8x+3=4x2-4xy+y2+4x-2y+1+x2+4x+4-2=(2x-y)2+2(2x-y)+1+ (x+2)^2-2=(2x-y+1)^2+(x+2)^2-2x+2 ,y为实数, ∴(2x-1+1)^2≥0 , (x+2)^2≥0 .W的最小值为-2,故答案为-2. ...
2-4xy+y2-2y+x2+8x+3=(4x2-4xy+y2)-2y+x2+8x+3=(2x-y)2-2y+x2+4x+4x+3=(2x-y)2+4x-2y+x2+4x+3=(2x-y)2+2(2x-y)+1-1+x2+4x+4-4+3=[(2x-y)2+2(2x-y)+1]+(x2+4x+4)-2=(2x-y+1)2+(x+2)2-2,∵x,y均为实数,∴(2x-y+1)2≥0,(x+2)2≥0,∴原...
答案解析 查看更多优质解析 举报 A-2B=5x^2y-3xy^2+4xy-2*(7xy^2-2xy+x^2y)=5x^2y-3xy^2+4xy-14xy^2+4xy-2x^2y=3x^2y-17xy^2+8xyx=1/2,y=-2代入A-2B=-1.5-34-8=-43.5 解析看不懂?免费查看同类题视频解析查看解答 更多答案(1) ...
(12)(4x2y-5y2x)-(3x2y-4xy2),其中x=--1,y=2\1(13)(x-3)2-x(x-8),其中x=2-4(14) (x+y)(x-Y)+(x-Y)²-(6x²y-2xy²)÷(2xy),当x=-2,y=1/3(15)(25a2-5a+1)(5a+1-5(1+2a)(2a-1)的值,其中a=2/5(16)-8x2-5x(-x+3y)+(3x+2y)(x-y),其中x=2,...
解答:解:A、3xy•(x2-2xy)=3xy•x2-3xy•2xy=3x3y-6x2y2,故本选项正确;B、2a2b•4ab3=2×4a2•a•(b•b3)=8a3b4,故本选项正确;C、5x(2x2-y)=5x•2x2-5x•y=10x3-5xy,故本选项正确;D、(2x-y)2=4x2-4xy+y2≠4x2+4xy+y2,故本选项错误.故选D. 点评:本题考查了单...