F.2 MATH Questions~Help~Fast~

believe 1) is [10cx - 5cy + 6x -3y] / [15cx + 9x]
= [(10cx+6x) - (5cy+3y)] / [3x(5c+3)]
= [2x(5c+3) - y(5c+3)] / [3x(5c+3)]
= [(2x-y)(5c+3)] / [3x(5c+3)]
= (2x-y) / (3x)

2011-12-01 11:38:09 補充：
believe 1) is [10cx - 5cy + 6x -3y] / [15cx + 9x]
= [(10cx+6x) - (5cy+3y)] / [3x(5c+3)]
= [2x(5c+3) - y(5c+3)] / [3x(5c+3)]
= [(2x-y)(5c+3)] / [3x(5c+3)]
= (2x-y) / (3x)

2.
1/(x-3) - 1/(3-x) + 2/(x+3)
= 1/(x-3) + 1/(x-3) + 2/(x+3)
= 2/(x-3) + 2/(x+3)
= 2[(x-3) + (x+3)] / [(x-3)(x+3)]
= 4x / [(x-3)(x+3)]

A1.
r = st / (s + t)
r(s + t) = st
rs + rt = st
rs = t(s - r)
t = (s - r) / (rs)

A2.
(1/x) - 2y + (1/z) = z
z - 2xyz + x = xz^2
xz^2 + 2xyz - x = z
x[z^2 + 2yz - 1] = z
x = z / [z^2 + 2yz - 1]