# Math Help - blurred

1. ## blurred

given that the cylinder has the equation x^2 +y^2 =ax where a is a constant. Why is the radius of this cylinder in polar coordinates?

2. Originally Posted by alexandrabel90
given that the cylinder has the equation x^2 +y^2 =ax where a is a constant. Why is the radius of this cylinder in polar coordinates?

$x^2+y^2=ax\iff \left(x-\frac{a}{2}\right)^2+y^2=\frac{a^2}{4}$ , so the cylinder's radius, in any coordinates, is $\frac{a}{2}$ ...what do you mean "in polar coordinates"?

Tonio

3. this is part of the range of an integral question and the answer was to integral the question where the radius runs from 0 to acos ( delta) and im wondering why that is the case.

the full question is here:
find the surface area of a hemisphere of a radius a cut off by a cylinder having the radius as diameter where the equation of the cylinder is x^2 +y^2 =ax.