1. ## Cube

A cube of edge 2cm is inscribed in a cylinder with an altitude of 4 cm. Find the volume of the cylinder?

2. Hello reiward
Originally Posted by reiward
A cube of edge 2cm is inscribed in a cylinder with an altitude of 4 cm. Find the volume of the cylinder?
Draw a plan view of the cube inscribed in the cylinder, and you'll get a square of side $\displaystyle 2$ cm inscribed in a circle. If the radius of the circle (and therefore also the cylinder) is $\displaystyle r$, then:
$\displaystyle r^2 = 1^2 + 1^2$
Now use the formula $\displaystyle V = \pi r^2 h$ to find the volume of the cylinder.

3. Can i use the formula

R = e / ( 2 sin theta/2 )
R = 2 / 2 sin 45

R = square rt of 2?

4. Hello reiward
Originally Posted by reiward
Can i use the formula

R = e / ( 2 sin theta/2 ) I'm not sure where this formula comes from...
R = 2 / 2 sin 45

R = square rt of 2? ...but this is certainly correct - see my last post: $\displaystyle \color{red}r^2 = 1^2+1^2$
Yes, $\displaystyle r = \sqrt2$. But, in fact, you need $\displaystyle r^2$ in the formula for the volume, so you don't need to take the square root.