Question

In △ABC AL is an angle bisector (L∈ BC ). Point M∈ AB so that LM=AM=BM. Find the angles in △ABC, if AC=2AL.

Answer 1

Since LM = AM, point M must be on the perpendicular bisector of AL. Since AM = BM, BL must be perpendicular to AL. This makes ∆ALC a right triangle with hypotenuse AC twice the length of side AL. Hence ∠LAC = ∠LAB = 60°, and AL is angle bisector, median, and altitude.

ΔABC is isosceles with ∠A = 120°, and ∠B = ∠C = 30°.