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## 7th grade foundations (Eureka Math/EngageNY)

### Unit 6: Lesson 2

Topic B: Foundations

# Types of triangles review

Review ways to classify triangles based on their sides lengths and angles.  Practice classifying triangles.

## Classifying triangles by their angles

### Acute triangles

An start color #11accd, start text, a, c, u, t, e, end text, end color #11accd triangle has start color #11accd, start text, 3, space, a, n, g, l, e, s, space, t, h, a, t, end text, end color #11accd start color #11accd, start text, e, a, c, h, space, m, e, a, s, u, r, e, space, l, e, s, s, space, t, h, a, n, space, end text, 90, degrees, end color #11accd. Below are examples of start color #11accd, start text, a, c, u, t, e, space, t, r, i, a, n, g, l, e, s, end text, end color #11accd.
A triangle with angle measures of 44 degrees, 68 degrees, and 68 degrees. The degree labels for all 3 angles are highlighted.
A triangle with angle measures of 60 degrees, 60 degrees, and 60 degrees. The degree labels for all 3 angles are highlighted.

### Right triangles

A start color #7854ab, start text, r, i, g, h, t, end text, end color #7854ab triangle has start color #7854ab, start text, 1, space, a, n, g, l, e, space, t, h, a, t, space, m, e, a, s, u, r, e, s, space, end text, 90, degrees, end color #7854ab and 2 acute angles. Below are examples of start color #7854ab, start text, r, i, g, h, t, space, t, r, i, a, n, g, l, e, s, end text, end color #7854ab.
A triangle with angle measures of 90 degrees, 45 degrees, and 45 degrees. The 90 degrees angle label is highlighted.
A triangle with angle measures of 90 degrees, 54 degrees, and 36 degrees. The 90 degrees angle label is highlighted.

### Obtuse triangles

An start color #1fab54, start text, o, b, t, u, s, e, end text, end color #1fab54 triangle has start color #1fab54, start text, o, n, e, space, a, n, g, l, e, space, t, h, a, t, space, m, e, a, s, u, r, e, s, end text, end color #1fab54 start color #1fab54, start text, m, o, r, e, space, t, h, a, n, space, end text, 90, degrees, end color #1fab54 and 2 acute angles. Below are examples of start color #1fab54, start text, o, b, t, u, s, e, space, t, r, i, a, n, g, l, e, s, end text, end color #1fab54.
A triangle with angle measures of 118 degrees, 31 degrees, and 31 degrees. The 118 degrees angle label is highlighted.
A triangle with angle measures of 104 degrees, 42 degrees, and 34 degrees. The 104 degrees angle label is highlighted.
Problem 1A
Classify triangle, P, Q, R by its angles.
A triangle PQR with angle measures of 112 degrees, 36 degrees, and 32 degrees.

Want to try more problems like this? Check out this exercise

## Classifying triangles by their side lengths

### Equilateral triangles

An start color #11accd, start text, e, q, u, i, l, a, t, e, r, a, l, end text, end color #11accd triangle has start color #11accd, start text, t, h, r, e, e, space, e, q, u, a, l, space, s, i, d, e, s, end text, end color #11accd. Below are examples of start color #11accd, start text, e, q, u, i, l, a, t, e, r, a, l, end text, end color #11accd triangles.
A triangle with side lengths of 10, 10, and 10 units.
A triangle with side lengths of 2, 2, and 2 units.

### Isosceles triangles

An start color #7854ab, start text, i, s, o, s, c, e, l, e, s, end text, end color #7854ab triangle has start color #7854ab, start underline, start text, a, t, space, l, e, a, s, t, end text, end underline, end color #7854ab start color #7854ab, start text, t, w, o, space, e, q, u, a, l, space, s, i, d, e, s, end text, end color #7854ab. Below are examples of start color #7854ab, start text, i, s, o, s, c, e, l, e, s, end text, end color #7854ab triangles.
A triangle with side lengths of 5, 5, and 4 units.
A triangle with side lengths of 5, 7, and 5 units.

### Scalene triangles

A start color #1fab54, start text, s, c, a, l, e, n, e, end text, end color #1fab54 triangle has start color #1fab54, start text, n, o, space, e, q, u, a, l, space, s, i, d, e, s, end text, end color #1fab54. Below are examples of start color #1fab54, start text, s, c, a, l, e, n, e, end text, end color #1fab54 triangles.
A triangle with side lengths of 6, 9, and 7 units.
A triangle with side lengths of 4, 7, and 5 units.
Problem 2A
Classify triangle, P, Q, R by its sides.
A triangle PQR. The angle at R has a box at its vertex connecting lines RP and RQ. Side RP is 5 units long, side RQ is 12 units long, and side PQ is 13 units long.