Question

The measures of two angles of pairs of triangles are given. Which pairs of triangles are similar?

Answer 1

Answer:

1, 2, and 5 are similar

Step-by-step explanation:

Answer 2

If the triangles are similar then the angles in both are equal. Let's look at each set individually:

(1) Triangle 1: 25°, 35°
Triangle 2: 25°, 120°
Now it may be hard to tell if the triangles are similar at the moment so we must calculate the third angle in each triangle (The angles in a triangle add up to 180°, therefor the missing angle = 180 - (given angle 1 + given angle 2)
Triangle 1: 180 - (25 + 35) = 120°
Triangle 2: 180 - (25 + 120) = 35°

Now writing out the set of angles again we have:
Triangle 1: 25°, 35°, 120°
Triangle 2: 25°, 120°, 35°

So in fact Triangle 1 and 2 are similar.

Now we can repeat this process for (2) - (5):

(2) Triangle 1: 100°, 60°, 20°
Triangle 2: 100°, 20°, 60°
This pair is also similar

(3) Triangle 1: 90°, 45°, 45°
Triangle 2: 45°, 40°, 95°
This pair is not similar

(4) Triangle 1: 37°, 63°, 80°
Triangle 2: 63°, 107°, 10°
This pair is not similar

(5) Triangle 1: 90°, 20°, 70°
Triangle 2: 20°, 90°, 70°
This pair is similar

Therefor pairs (1), (2) and (5) are similar