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10th grade The Triangle Proportionality (side-splitting) Theorem worksheet

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The Triangle Proportionality (side-splitting) Theorem

Grade 10 Math Worksheet

NameDate

Circle the best answer, or write your answer on the line.

  1. Noah adds a beam GH to a roof front. In △CDF, GH ∥ DF, with G on CD and H on CF. How long is HF, in feet?

  2. Pia plans a path GH across a triangle park. In △CDF, GH ∥ DF, with G on CD and H on CF. How long is HF, in meters?

  3. Tala builds a ramp with a brace GH. In △CDF, GH ∥ DF, with G on CD and H on CF. What is x?

  4. Zee maps a road GH across a triangle of streets. In △CDF, GH ∥ DF, with G on CD and H on CF. What is x?

  5. Ari cuts a wedge of cheese along GH. In △CDF, GH ∥ DF, with G on CD and H on CF. What is x?

  6. Bo glues a strip GH across a triangle window. In △CDF, GH ∥ DF, with G on CD and H on CF. What is x?

  7. Esme checks whether a tent's crossbar GH is level with the ground DF. G is on CD and H is on CF. Is GH ∥ DF?

    • No: CG = 4 but CH = 6
    • Not enough: GH and DF are needed
    • No: the gaps 2 and 3 are different
    • Yes: 6/4 = 9/6 = 3/2
  8. Jun checks whether a ramp brace GH runs beside the ground DF. G is on CD and H is on CF. Is GH ∥ DF?

    • Yes: both bottom pieces are 2 longer
    • No: 7/5 but 9/7
    • Yes: 7/5 and 9/7 both put the bottom piece on top
    • Not enough: GH and DF are needed
  9. Kira checks whether a ladder's spreader bar GH runs beside the floor DF. G is on CD and H is on CF. Is GH ∥ DF?

    • No: CG = 3 but CH = 4
    • Not enough: GH and DF are needed
    • Yes: 6/3 = 8/4 = 2
    • No: the gaps 3 and 4 are different
  10. Luz checks whether a roof beam GH runs beside the ceiling DF. G is on CD and H is on CF. Is GH ∥ DF?

    • No: 6/4 = 3/2 but 8/6 = 4/3
    • Yes: both bottom pieces are 2 longer
    • Yes: 6/4 and 8/6 both put the bottom piece on top
    • Not enough: GH and DF are needed
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10th grade The Triangle Proportionality (side-splitting) Theorem worksheet – printable
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About this worksheet

The Triangle Proportionality Theorem. Every version has 10 questions, and the answer key prints on the second page.

What your child will learn

  • I can say that a line parallel to one side cuts the other two sides into pieces with the same ratio.
  • I can find a missing piece, also from a whole side or with x, and tell from four pieces whether a segment is parallel to a side.
  • I can use an angle bisector to split the opposite side in the ratio of the other two sides.

Standard: G-SRT.B.4

Words to know

parallel (∥): Running the same way and never meeting; arrows on a sketch show it.

piece: Part of a side, from a corner to the point where the line crosses it.

whole side: The full side from corner to corner: the two pieces added.

proportion: Two equal ratios, such as CG : GD = CH : HF.

converse: The theorem turned around: equal ratios show the line is parallel.

angle bisector: A segment from a corner that cuts its angle into two equal angles.

Common mistakes

Your child added or took away the same amount on both sides instead of using one multiplier.

Your child used the multiplier upside down, so a longer piece came out shorter.

Your child wrote one ratio top over bottom and the other bottom over top.

What to say

Ask: does a parallel line cut both sides by the same amount or in the same ratio?

Ask: on side CD, which piece is longer, the top or the bottom?

Ask: does each fraction start with the top piece?

Questions parents ask

What is the most common mistake with the triangle proportionality (side-splitting) theorem?

Your child added or took away the same amount on both sides instead of using one multiplier.

How can I help my child with the triangle proportionality (side-splitting) theorem?

Ask: does a parallel line cut both sides by the same amount or in the same ratio?

Are these 10th grade math worksheets free to print?

Yes. All 6 printable versions at each level are free to print, with the answer key, and no account is needed.

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