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Math Help - Cube

  1. #1
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    Cube

    A cube of edge 2cm is inscribed in a cylinder with an altitude of 4 cm. Find the volume of the cylinder?
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  2. #2
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    Hello reiward
    Quote Originally Posted by reiward View Post
    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 2 cm inscribed in a circle. If the radius of the circle (and therefore also the cylinder) is r, then:
    r^2 = 1^2 + 1^2
    Now use the formula V = \pi r^2 h to find the volume of the cylinder.

    Grandad
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  3. #3
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    Can i use the formula

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

    R = square rt of 2?
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  4. #4
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    Hello reiward
    Quote Originally Posted by reiward View Post
    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: \color{red}r^2 = 1^2+1^2
    Yes, r = \sqrt2. But, in fact, you need r^2 in the formula for the volume, so you don't need to take the square root.

    Grandad
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