Draw a line parallel to distance between two buildings
then we get triangle in which side are
Hypotenuse=15
opposite=20-8
=12
adjacent=?
by Pythagoras,
(hypotenuse)²=(Opposite)²+(adjacent)²
15²=12²+adj²
225-144=adj²
81=adj²
9=adjacent
so the distance between two buildings is 9ft
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