dstao
幼苗
共回答了17个问题采纳率:76.5% 举报
1.
已知X+Y=12,XY=9.求x^2y+2xy^2分之x^2+3xy+2y^2
(x^2+3xy+2y^2 )/(x^2y+2xy^2)
=(x+2y)(x+y)/xy(x+2y)
=(x+y)/xy
=12/9
=4/3
2.
已知3分之x=4分之y=5分之z(z不等于0),求x^2+y^2+z^2分之xy+yz+zx.
令3分之x=4分之y=5分之z=k
那么x=3k ,y=4k ,z=5k
(xy+yz+zx)/(x^2+y^2+z^2)
=(3k*4k+4k*5k+5k*3k)/(9k^2+16^2+25k^2)
=(12k^2+20k^2+15k^2)/(9k^2+16^2+25k^2)
=47k^2/50k^2
=47/50
3.
已知a分之1-b分之1=3,求a-b-ab分之2a-2b+3ab.
a分之1-b分之1=3,那么(b-a)/ab=3,b-a=3ab
(2a-2b+3ab)/(a-b-ab)
=[2(a-b)+3ab]/(a-b-ab)
=(-3ab*2+3ab)/(-3ab-ab)
=-3ab/-4ab
=3/4
4.
已知x^2-3x+1=0,求x^2+x^2分之1
x^2-3x+1=0,那么x^2+1=3x(同时除以x)
x+1/x=3
x^2+1/x^2
=(x+1/x)^2-2
=3^2-2
=7
1年前
10