F.2 MATHS

1. 1/x-1-1/x
=x(1)/x(x-1)-1(x-1)/x(x-1)
=x/x(x-1)-x+1/x(x-1) 找最小公倍數
=1/x(x-1)
2.x/x+y +y/x-y
=x(x-y)/(x+y)(x-y) +y(x+y)/(x+y)(x-y)
=x^2-xy/(x+y)(x-y)+xy+y^2/(x+y)(x-y) Don't expand the denominator
=x^2+y^2/(x+y)(x-y)

唔知對不對,自己驗算