LaTeX

Hey guys. Sorry to bother you. I am trying to learn LaTeX, and I found a
little question. I am trying to write the classic wave equation
(d^2f/dx^2)=-(2pi/lambda)^2f(x)  and I want to enclose the fraction in
brackets, but the brackets are too small. how do I make big brackets?  I
found this: Bigl( and Bigr)   but Even thhat isn't big enough.

Thanks.