I have 2 problems that i am stuck on

1) Find a set of cylindrical coordinates (withr≥ 0 and 0 ≤θ< 2π) of the point whose Cartesian coordinates are given. (-5, -5, -4)

i have already found r and z, which are (5sqrt(2), ? ,-4) and have confirmed that those 2 are correct but i cannot find the right answer for theta.

This is what i have tried but it is not the correct answer and i do not know why.

y/x=tan(theta)

theta = arctan(-5/-5)

theta = arctan(1) = pi/4 (wrong?!?!?! why?!?!)

2) Find a set of spherical coordinates (withρ≥ 0, 0 ≤ϕ≤πand 0 ≤θ< 2π) of the point whose Cartesian coordinates are given.(0, – 5√3, 5)

On this one, i already solved for rho and p but not for theta.

(10, arctan((sqrt(75))/5) , ? )

This is what i have tried but i dont understand how you can divide by zero.

tan(theta) = y/x

theta = arctan(5sqrt(3)/0) (divide by zero?!?! what?!?!)

Can anyone help? THANKS!!