An isosceles triangle’s altitude will bisect its base. which expression could be used to find the area of the isosceles triangle above?

The Correct Answer is (E) — Recall that congruent means that two polygons are the same shape and size. Since ∆ABC and ∆ACD are congruent, you know that each angle from one triangle corresponds to an angle of the other triangle. If you are having a hard time visualizing the triangles matching up, mark up the given diagram or draw your own to show the triangles side by side:

Just by filling in the angles, you can see that the remaining angle in each triangle must be 60°. To find ∠BCD, simply sum ∠BCA and ∠ACD to get a total of 60° + 90° = 150°.

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