How do I finish this polar equations problem?

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SUMMARY

The discussion focuses on solving the polar equation r = 3cos(θ) to find points where the tangent is horizontal or vertical. The derivative d/dθ = -3sin(θ) is calculated, leading to the equation 3cos(2θ) = 0, which yields θ values of π/4 and 3π/4. The participants clarify how to derive the corresponding r values, resulting in points (3/√2, π/4) and (-3/√2, π/4). This solution effectively identifies critical points on the polar curve.

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Homework Statement



Find the points on the given curve where the tangent is horizontal or vertical

Homework Equations



r = 3cos(θ)

The Attempt at a Solution



d/dθ = -3sin(θ)

for horizontal:

-3sin(θ)sin(θ) + 3cos(θ)cos(θ)

I used identity and got:

3cos(2θ) = 0

I got the values PI/4, 3PI/4

How do I get the values 3/sqrt(2) and -3/sqrt(2)

to give me points (3/sqrt(2), Pi/4) and (-3/sqrt(2), Pi/4)
 
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You found some values for ##\theta##. Use the equation you started with to get the corresponding values for ##r##.
 

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