To solve this problem you must apply the proccedure shown below:
1. You have to rewrite x=12 in polar form. Then, you have:
12=rCosθ
2. Then, you must solve for r, as following:
r=12/Cosθ
3. You have that 1/Cosθ=Secθ, therefore:
r=12(1/Cosθ)
r=12Secθ
Therefore, as you can see, the answer is: r=12Secθ
