Trig Help Finding the Length of the Slope of a Pyramid

njbeep

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Aug 15, 2016
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Hi there,

I am struggling to work out what i've misunderstood in the following question (working out and image below).

The total height of the shape below is 15 cm. Calculate the length of the sloping side of the pyramid.

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My working out is as follows:

I figured that the base is like a diameter, 11/2 = 5.5 cm
I figured that we subtract the 5 cm length from the cuboid away to give us our height 15 cm - 5 cm = 10 cm.

a^2 + b^2 = c^2
10^2 + 5.5^2 = c^2
100 +30.25 = c^2
c = sqrt130.25
c = 11.41 cm

The answer in the back of the book is wildly different, it's 12.67 cm.
Any explanation will be greatly appreciated.
 

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It comes down to how you interpret the "sloping side of the pyramid". I agree with your interpretation, by the way.

The answer the book gives is the length of the sloping edge of the pyramid. (Using Pythagoras' rule to find the hypotenuse using your result of 11.41 as height and 5.5 as base.)
 
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