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8th grade Are these triangles similar? (angle-angle) worksheet

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Are these triangles similar? (angle-angle)

Grade 8 Math Worksheet

NameDate

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

  1. Pia compares two kite panels, A and B. Are the two triangles similar?

    • No: the first angles are 41° and 59°, so the two kite panels are not similar
    • Yes: both have the angles 41°, 59° and 80°, so they are similar
    • Not enough to tell: we need the side lengths first
  2. Ren compares two gable ends, A and B. Are the two triangles similar?

    • No: the first angles are 36° and 64°, so they are not similar
    • Yes: both have the angles 36°, 64° and 80°, so they are similar
    • Not enough to tell: we need the side lengths first
  3. Tala compares two mainsails, A and B. Are the two triangles similar?

    • Not enough to tell: we need the side lengths first
    • No: A's angles are 38° and 67° but B's are 38° and 75°, so they are not similar
    • Yes: both have the angles 38°, 67° and 75°, so they are similar
  4. Zee compares two tent flaps, A and B. Are the two triangles similar?

    • No: A's angles are 44° and 56° but B's are 56° and 80°, so they are not similar
    • Yes: both have the angles 44°, 56° and 80°, so they are similar
    • Not enough to tell: we need the side lengths first
  5. Bo checks two triangle warning signs, A and B. Are the two triangles similar?

    • Yes: both have a 48° angle, so they are similar
    • No: A's angles are 48°, 62° and 70° but B's are 48°, 57° and 75°, so they are not similar
    • Not enough to tell: we need the side lengths first
  6. Kira compares two kite wings, A and B. We only know that each has a 50° angle. Are the triangles similar?

    • Not enough to tell yet: we need a second pair of equal angles
    • Yes: they have an equal angle, so the two triangles are similar
    • No: one equal angle means they are not similar
  7. Luz compares two paper triangles, A and B. We only know that each has a 90° angle. Are the triangles similar?

    • Yes: they share an equal angle, so the two triangles are similar
    • Not enough to tell yet: we need a second pair of equal angles
    • No: one equal angle means they are not similar
  8. Milo compares two tents, A and B. We only know that each has a 70° angle. Are the triangles similar?

    • Not enough to tell yet: we need a second pair of equal angles
    • No: one equal angle means they are not similar
    • Yes: they have one equal angle, so the two triangles are similar
  9. Pia cuts two right-triangle sails, A and B. How many cm long is B's side across the 37° angle?

  10. Zee cuts two right-triangle tents, A and B. How many cm long is B's side across the 53° angle?

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8th grade Are these triangles similar? (angle-angle) worksheet – printable
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About this worksheet

Are these triangles similar? (two equal angles). Every version has 10 questions, and the answer key prints on the second page.

What your child will learn

  • I can tell whether two triangles are similar from their angles alone: two equal angles are enough, because the third angles must match too.
  • I can find a triangle's third angle, including in an isosceles or a right triangle, and match corners and sides by their equal angles.
  • I can use the equal angles to pair the sides across them and find a missing side.

Standard: 8.G.A.5 (angle-angle criterion), 8.G.A.4 (partial)

Words to know

similar triangles: Same shape, maybe different size: the angles match and the sides grow by one number.

third angle: The angle left over: 180° minus the other two.

matching corners: Corners with equal angles, in the same place on each triangle.

across from an angle: The side that sits opposite that corner, not touching it.

isosceles triangle: A triangle with two equal sides. Its two base angles are equal.

right triangle: A triangle with one 90° angle. Its other two angles add to 90°.

similarity statement: A sentence like "triangle CDF is similar to triangle WVU". Its letters pair up in order.

Common mistakes

Matched angles, corners or sides by where they sit in a list or in the alphabet, not by their size.

Thought one equal angle is enough to call two triangles similar. Draw two different triangles that both have a 50° angle and compare them.

Thought we need the side lengths to tell whether two triangles are similar.

What to say

Ask: which angle in the second triangle is equal to this one?

Ask: if two angles of one triangle equal two angles of the other, what must the third angles be?

Questions parents ask

What is the most common mistake with are these triangles similar? (angle-angle)?

Matched angles, corners or sides by where they sit in a list or in the alphabet, not by their size.

How can I help my child with are these triangles similar? (angle-angle)?

Ask: which angle in the second triangle is equal to this one?

Are these 8th 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.

More grade 8 math

See all grade 8 math

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