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Supplementary angles worksheets

Find one missing angle in 6, 8 or 10 supplementary pairs using whole numbers, tenths or hundredths. Each numbered straight-line diagram identifies the given and unknown regions clearly.

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Find the missing measure in each supplementary pair. The two regions total 180 degrees. Diagrams are not to scale.

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Use exact angle relationships to deduce each blank

Each numbered region connects the diagram to one printed measure or blank. Complementary regions total 90 degrees, supplementary regions on a straight line total 180 degrees, and opposite vertical regions are equal.

The diagrams preserve those relationships but are not drawn to the stated values. Use subtraction or vertical-angle equality, then check the result against the 90-degree or 180-degree total instead of measuring the picture.

Learning objective

What this activity builds

Use the 180-degree total of a supplementary pair to calculate a missing measure across the full nondegenerate decimal domain.

Worked example

Region 2 measures 126.35 degrees on a straight line. What is Region 1?

53.65 degrees.

Supplementary angles add to 180 degrees. Compute 180.00 - 126.35 = 53.65, then check that the two stated measures sum to 180.00.

Teaching notes

Make the practice count

  • Identify the straight line first so the 180-degree total has a geometric reason.
  • Have learners predict whether the unknown is acute, right or obtuse before calculating.
  • Align decimal points and preserve the worksheet precision in the final answer.
  • Verify every answer by addition rather than judging the representative diagram by eye.

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Math SheetNameScore/ 8TeacherDateSupplementary anglesFind the missing measure in each supplementary pair. Diagrams are not to scale.1.12Region 1:8°Region 2:______°2.12Region 1:______°Region 2:5°3.12Region 1:______°Region 2:67°4.12Region 1:______°Region 2:171°5.12Region 1:145°Region 2:______°6.12Region 1:104°Region 2:______°7.12Region 1:74°Region 2:______°8.12Region 1:______°Region 2:102°math-sheet.comPage 1 / 1

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