x+y=1.5 15x+5y=20

x+y=5; x^y+y^x=17 已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y) 解方程组 x+2y=1.5,12(x+y)+15y=20 先化简再求值(x-y)(x+y)-(x-2y) 的完全平方+x(3x-5y)-(x-y)(x-2y),其中x=1/2 y Y={X (-5 解方程x+y+(x+y/2)=15 3x+5y+4(x+y/2)=62 10/x+y+3/x-y=-5 15/x+y-2/x-y=-1（用换元法解此方程组） 已知：x-y=1,x+y=-7,求代数式3（x+y)+20(x-y)-5的值 x+y/2+x-y/3=6,4(x+y)-3(x-y)=-20 {(x+y)/2+(x-y)/3=6 4(x+y)-3(x-y)=-20 4(x+y)-3(x-y)=-20,2/x+y+3/x-y=6 6(x-y)-2(x+y)=14 3(x-y)+(x+y)=5