$\tfrac{1}{P_1}+\tfrac{1}{q_1}=\tfrac{1}{f_1}$

how to write equations in this forum? it is cool but i dont think it is default in SMF right?
[code]$\tfrac{1}{P_1}+\tfrac{1}{q_1}=\tfrac{1}{f_1}$[/code]