Videos and solutions to help Grade 8 students learn to present informal arguments as to whether or not two triangles are similar and how to find lengths of corresponding sides of similar triangles.

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Lessons for Grade 8

Common Core For Grade 8

• Students present informal arguments as to whether or not two triangles are similar.

• Students practice finding lengths of corresponding sides of similar triangles.

• Given just one pair of corresponding angles of a triangle as equal, use the side lengths along the given angle to
determine if triangles are in fact similar.

• Given similar triangles, use the fact that ratios of corresponding sides are equal to find any missing measurements.

Classwork

Example 1 & 2

Given the information provided, is △ ABC ∼ △ DEF?

Example 3

Given that △ ABC ∼ △ AB'C', could we determine the length of AB'?

Example 4

If we suppose XY is parallel to X'Y', can we use the information provided to determine if △ OXY ∼ △ OX'Y'?

Explain.

Example 5

Given the information provided, is △ OPQ ∼ △ Op'Q'?

Exercises

1. In the diagram below, you have △ ABC and △ AB'C'.

Use this information to answer parts (a)–(d).

a. Based on the information given, is △ ABC ∼ △ AB'C'? Explain.

b. Assume line BC is parallel to line B'C'. With this information, can you say that △ ABC ∼ △ AB'C'. Explain.

c. Given that △ ABC ∼ △ AB'C' determine the length of AC'.

d. Given that △ ABC ∼ △ AB'C' determine the length of AB.

2. In the diagram below, you have △ ABC and △ A'B'C'.

Use this information to answer parts (a)–(c).

a. Based on the information given, is △ ABC ∼ △ A'B'C'? Explain.

b. Given that △ ABC ∼ △ A'B'C' determine the length of A'C'.

d. Given that △ ABC ∼ △ A'B'C' determine the length of BC.

3. In the diagram below, you have △ ABC and △ A'B'C'. Use this information to answer the question below. Based on the information given, is △ ABC ∼ △ A'B'C'?

Explain.

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