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Alternate Angles Worksheets

Find two missing alternate interior angles on marked parallel-line diagrams, with whole degrees, tenths or hundredths.

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Find the two missing angles. The matching arrow marks show parallel lines. Alternate interior angles are equal.

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Look inside the parallel lines

Alternate interior angles lie between the parallel lines on opposite sides of the transversal, and their measures are equal.

Learning objective

What this activity builds

Use equal alternate interior angles to find missing angle measures.

Worked example

Alternate interior angles 1 and 3 are equal. Angle 3 is 64.5 degrees. Find angle 1.

64.5 degrees.

The marked lines are parallel, so the alternate interior angle has the same measure: angle 1 = angle 3 = 64.5 degrees.

Teaching notes

Make the practice count

  • Interior angles lie between the parallel lines.
  • Alternate interior angles lie on opposite sides of the transversal.
  • Match each blank with its equal given angle before calculating.

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Six parallel-line diagrams each give one angle from both alternate-interior equality pairs and ask for their direct partners. Both transversal slopes appear.

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Math SheetNameScoreTeacherDateAlternate AnglesUse the marked parallel lines to find the two missing alternate interior angles.1. Find angles 1 and 4.Given: A2 = 147 deg; A3 = 33 deg1234A1, A4:2. Find angles 2 and 3.Given: A1 = 120 deg; A4 = 60 deg1234A2, A3:3. Find angles 2 and 3.Given: A1 = 37 deg; A4 = 143 deg1234A2, A3:4. Find angles 1 and 4.Given: A2 = 74 deg; A3 = 106 deg1234A1, A4:5. Find angles 1 and 2.Given: A3 = 144 deg; A4 = 36 deg1234A1, A2:6. Find angles 1 and 2.Given: A3 = 48 deg; A4 = 132 deg1234A1, A2:Alternate interior angles are equal when a transversal crosses parallel lines.math-sheet.comPage 1 of 1

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