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6th grade · Math · Unit 12 of 19

Angles & Triangles

Measure, classify, find missing angles

What your child practices

Estimating and classifying angles (acute, right, obtuse, straight, reflex), finding missing angles on a line and in triangles, and classifying triangles by their sides and angles.

Texas Essential Knowledge and Skills (TEKS) teks student expectation: 6.8(A) · the angle sum of a triangle and classifying triangles

How we explain it

Children can open this short lesson before they practice.

  1. Angles are measured in degrees. A right angle is 90°, a straight line is 180°.
  2. The three angles in any triangle add to 180°.
  3. Acute is under 90°. Obtuse is between 90° and 180°.

Example: A triangle has angles of 50° and 70°. What is the third angle? 50 + 70 = 120. 180 − 120 = 60. Answer: 60°

Angles & Triangles in Texas

In the Texas Essential Knowledge and Skills (TEKS), this is unit 12 of 19 in 6th grade Math, after Equations and before Perimeter & Area.

Gradelings describes a child's practice on this unit as Beginning, Approaching, Meeting or Exceeding (Four practice steps). That reflects practice, not a report-card mark: the teacher decides the mark.

Source: Texas Education Agency (TEA)

Sample questions

A taste of this unit. In the app, questions change every time and get easier or harder to match your child.

  1. Question 1

    A triangle has angles of 50°, 85° and 45°. Classify it by its angles.

    • acute triangle
    • obtuse triangle
    • right triangle

  2. Question 2

    About how many degrees is this angle?

    • 330°
    • 285°
    • 150°
    • 30°

  3. Question 3

    An isosceles triangle has two equal base angles. Its third angle is 120°. What is each base angle?

    answer box°

  4. Question 4

    A triangle has sides of 9 cm, 7 cm and 7 cm. What type of triangle is it?

    • equilateral
    • isosceles
    • scalene

  5. Question 5

    Two angles of a triangle are 37° and 30°. What is the third angle?

    answer box°

  6. Question 6

    This angle measures 90°. What kind of angle is it?

    • obtuse
    • acute
    • right
    • straight
    • reflex

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