Changing rectangular to cylindrical

[eurekameh]

Change (-3,3,3) to cylindrical coordinates.
I'm doing r^2 = x^2 + y^2, which I find r = sqrt(18) = 3radical(2)
tan(theta) = 3/-3 = 1, so theta = -pi/4 = 7pi/4.
z = 3
Cylindrical coordinates are (3sqrt(2),7pi/4,3).
Is this right? Correct answer to the homework says 3pi/4 for the angle, for some reason.

 

[Mark44]

Change (-3,3,3) to cylindrical coordinates.
I'm doing r^2 = x^2 + y^2, which I find r = sqrt(18) = 3radical(2)
tan(theta) = 3/-3 = 1, so theta = -pi/4 = 7pi/4.

The angle θ is in the 2nd quadrant, so 3\pi/4 is correct.

z = 3
Cylindrical coordinates are (3sqrt(2),7pi/4,3).
Is this right? Correct answer to the homework says 3pi/4 for the angle, for some reason.

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