You can find the number of x intercepts by setting f(x) equal to zero giving you 0=x^4-5x^2. You can factor out an x^2 and divide on both sides (when you divide 0 by anything it is still zero so the x^2 disappears), and you are left with 0=x^2-5, which you can solve easily giving you x=+/- sqrt(5). However, the original equation also has an x intercept at (0,0) which you can see by plugging 0 in for x. So the grand total of x intercepts is 3!
