# geometry

the base of an isosceles triangle is 18 centimeters long. The altitude to the base is 12 centimeters long. What is the approximate measure of a base angle of the triangle?

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1. Since it is isosceles, the altitude splits it into two congruent right triangles. The base angle is
arctan(12/9) = arctan(4/3). It's a "3,4,5" right triangle. Use a table or calculator to get the angle. It's about 53 degrees

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2. The altitude of an isosceles triangle
is the perpindicular bisector of the
base and devides the triangle into 2
congruent rt. triangles. Y=12=altitude, X=18/2=9= 1/2 of base.
TanB=Y/X=12/9=1.3333, B=53.13 Degrees.

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