Question 160405
Since the shape of a TV is rectangular, the corners are all 90 deg (right angles).  This means we can apply Pythagorean Theorem.
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Additionally, when the say a "25 in. TV", the 25 inches they are referring to is measured along the diagonal of the TV.
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Let h = height of TV
then
25^2 = h^2 + 20^2
625 = h^2 + 400
225 = h^2
15 inches = h (height)