1.0.5(x-0.2)=0.9x-1.78 2.x/3=(2x-11)/5 3.｛x+y=9 ｛6x+7y=59

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1.0.5(x-0.2)=0.9x-1.78 2.x/3=(2x-11)/5 3.｛x+y=9 ｛6x+7y=59
第三题是一起的

1.
0.5(x-0.2)=0.9x-1.78
0.5x-0.1=0.9x-1.78
0.5x=0.9x-(1.78-0.1)
0.5x=0.9x-1.68
0.9x-0.5x=1.68
0.4x=1.68
x=1.68/0.4
x=4.2
2.
x/3=(2x-11)/5
6x-33=5x
6x-5x=33
x=33
3.
｛x y=9 (1) ｛6x 7y=59 (2)
(1)*7=7x＋7y=63
7x＋7y-6x-7y
=(7x-6x)＋(7y-7y)
=x-0
=x
x=63-59
x=4
y=9-4
y=5
再问：第三题有些不懂

y=(x-1)(x-2)(x-3)(x-4)(x-5)(x-6)(x-7)(x-8)(x-9)(x-10)的导数在x=1 用递归法求y=x-(x*x*x/3!)+(x*x*x*x*x/5!)-(x*x*x*x*x*x*x/7!)+. 若2x-3y+4=0则x（x*x-1)+x(5-x*x)-6y+7 已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y) 3(x+y)-4(x-y)=11,2(x-y)+5(x+y)=27 6(x-y)-2(x+y)=14 3(x-y)+(x+y)=5 x+y=3 x+2y=9 3/x+1=y y-x=3 y=2x-3 y-3x=1 2(x+1)-y=6 7x-5y=-9 3x+2=y 5X+4=Y 7X+6=Y 9X+8=y 11x=y要如何计算 3x+2=y 5x+4=y 7x+6=y 9x+8=y 11x=y y-3x=2,y-5x=4,y-7x=6,y-9x=8,y-11x=0方程组, 3x+2=y 5x+4=y 7x+6=y 9x+8=y 11x=y 联立方程有的话先化简再求值(x-y)(x+y)-(x-2y) 的完全平方+x(3x-5y)-(x-y)(x-2y),其中x=1/2 y