有數學唔識

1.f / 4e + f / 6e
=3f / 12e + 2f /12e
=5f/12e

2 .(x + 2y) / 3x - y/6x
= (2x + 4y) / 6x - y / 6x
=(2x + 3y) / 6x
= 1/3 x + 1/2 y


3.(2u) /(u+v) + v / (u-v)
= (2u) (u-v) / (u+ v)(u-v) + v(u+v) /(u+v)(u-v)
=( 2uu - 2uv +uv+vv) / (u+v)(u-v)
= (2uu - uv +vv) / (u+v)(u-v)
= (v + u)(v-2u) / (u+v)(u-v)
= (v-2u) / (u-v)