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

6 printable versionsBuilding Confidence10 questions · answer keyFree · no account

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Are these triangles similar? (angle-angle)

Grade 8 Math Worksheet - Building Confidence

NameDate

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

  1. Ari sees triangle A on a tent flap. A has a 42° angle and a 63° angle. The sketch writes 180° beside the triangle. What is A's third angle?

  2. Kira enlarges a small sail A into a big sail B. The scale factor from A to B is 3. How many cm long is B's side across the 40° angle?

  3. Noah enlarges a small tent front A into a big tent front B. The scale factor from A to B is 4. How many cm long is B's side across the 55° angle?

  4. Pia compares a small sail A and a big sail B. Are the two triangles similar?

    • Not enough to tell: we need the side lengths first
    • Yes: all three angles match, so they are similar
    • No: B is much bigger than A, so they are not similar

  5. Ren compares a small roof A and a big roof B. Are the two triangles similar?

    • No: the lists start with 40° and 75°, so they are not similar
    • Not enough to tell: we need the side lengths first
    • No: B is much bigger than A, so they are not similar
    • Yes: all three angles match, so they are similar

  6. Tala compares a small tent A and a big tent B. Are the two triangles similar?

    • No: B is much bigger than A, so they are not similar
    • Yes: all three angles match, so they are similar
    • No: the lists start with 30° and 80°, so they are not similar
    • Not enough to tell: we need the side lengths first

  7. Zee compares two kite wings, A and B. Are the two triangles similar?

    • Yes: both have a 40° angle, so they are similar
    • No: the angles do not all match, so they are not similar
    • Not enough to tell: we need the side lengths first

  8. Bo compares two triangle warning signs, A and B. Are the two triangles similar?

    • No: the angles do not all match, so they are not similar
    • Yes: both have a 25° angle, so they are similar
    • Not enough to tell: we need the side lengths first

  9. Esme compares a small paper pennant A and a big paper pennant B. Are the two triangles similar?

    • No: B is much bigger than A, so they are not similar
    • No: the lists start with 35° and 50°, so they are not similar
    • Not enough to tell: we need the side lengths first
    • Yes: all three angles match, so they are similar

  10. Noah labels the corners of two similar kites. Triangle WYC is the small one and triangle DFG is the big one. Which corner of DFG matches corner Y?

    • corner D
    • corner G
    • corner F
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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

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