Question 169900
What is the base length of an isosceles triangle that has two legs of 5 inches and the obtuse angle of 120 degres and the two base angles of 30 degress? 
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If you sketch this, then draw the altitude from the upper vertex (=120 degs), you see that 5 is the hypotenuse of each of 2 congruent triangles.  Half of the base is 5*cos(30) = 5*sqrt(3)/2.  So the base is 5*sqrt(3), = ~8.6603