Parametric Equation Question Ok this is a really silly question and I should know this, but I can't seem to figure something out:
for the last step, how do they know that $0 \leq x \leq 4$? If we use the minimum value of theta, which is $-\pi/2$, and plug that into $x=\cos(\theta)$, then we get $0$, and same for $\pi/2$.

Well, y^2 has to be positive, so the minimum that y^2/25 could be is 0.  So, x^2/16 is 1 at the maximum => x≤4.  The same argument applies for x = 0
