text: question involving isosceles triangle? the sides of an isosceles triangle measure 14, 14, and 18. find the degree measure of the base angles.  a, 50 degrees    b, 80 degrees   c, 90 degrees    d,120 degrees  i don't understand how to do this.  i already omitted answer choices c and d because they are base angles, and 90 + 90 would leave no measure for the third angle, and 120+120 is over the sum of the angles in a triangle.  i just need someone to tell me how to do it.  thanks if it is an isosceles triangle, and you drop a height from the angle between the 14's, then you're creating two right triangles with hypotenuse 14 and one leg 9 (the height bisects the base of the triangle).  using some trig, you can find the base angle.  from the point of view of that angle, 9 is an adjacent side, and 14 is a hypotenuse.  so,  cos x = 9/14 cos x = 0.6429 x = 50 (look it up in a table or use your cos^(-1) function on your calculator)  so your answer is (a).