Why is z = rcos(θ) and not z = rsin(θ) in surface integrals?

[Miike012]

Look in the paint doc. I was wondering why they said z = rcos(θ) and not z = rsin(θ) and x = rcos(θ)

 

[haruspex]

The set-up is symmetric between x and z, so does it matter which is equated with the cos and which with the sin?

 

[Miike012]

The set-up is symmetric between x and z, so does it matter which is equated with the cos and which with the sin?

Well when i used sine I came out with a different answer but ill try again.

 

[Miike012]

The set-up is symmetric between x and z, so does it matter which is equated with the cos and which with the sin?

You are right the answers are the same. thanks.