數學問題，唔識做，幫一幫手

f(x)=(x+1)/(x-1)
f[(x+1)/(x-1)]
=[(x+1)/(x-1) + 1 ] / [(x+1)/(x-1) - 1 ] <----------------------substitution
=[(x+1)/(x-1) + (x-1)/(x-1)] / [(x+1)/(x-1) - (x-1)/(x-1)] <--change 1 to (x-1)/(x-1)
={ [(x+1)+(x-1)]/(x-1) } / { [(x+1)-(x-1)]/(x-1) } <-----------add/subtract the fractions
=[(x+1)+(x-1)] / [(x+1)-(x-1)] <--------------------------------multiply x-1 to both sides
=(x+1+x-1) / (x+1-x+1) <---------------------------------------brackets
=2x/2 <------------------------------------------------------------add/subtract the terms
=x

f [(x + 1) / (x - 1)]
= {[(x + 1) / (x - 1)] + 1} / {[(x + 1) / (x - 1)] - 1}
= [(x + 1) + (x - 1)] / [(x + 1) - (x - 1)]
= (x + 1 + x - 1) / (x + 1 - x + 1)
= 2x / 2
= x