Grade 8 · Math

8th grade Can three lengths make a triangle? worksheet

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Can three lengths make a triangle?

Grade 8 Math Worksheet - Challenge Me

NameDate

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

Jun cuts paper strips for an isosceles triangle. The base is 9.4 cm, and each equal side is a whole number of cm. What is the shortest each equal side can be?
Kira cuts paper strips for an isosceles triangle. The base is 12 cm, and each equal side is a whole number of cm. What is the shortest each equal side can be?
Luz cuts pieces of yarn for an isosceles triangle. The base is 7 cm, and each equal side is a whole number of cm. What is the shortest each equal side can be?
Noah cuts paper strips of (x + 2) cm, 7 cm and 12 cm for a triangle. So x is more than ? and less than ?. Type both numbers, smaller first.
Pia cuts pieces of yarn of (x + 3) cm, 5.5 cm and 9 cm for a triangle. So x is more than ? and less than ?. Type both numbers, smaller first.
Ren cuts paper strips of (x − 1) cm, 6 cm and 10 cm for a triangle. So x is more than ? and less than ?. Type both numbers, smaller first.
Tala cuts pieces of yarn of 2x cm, 8 cm and 14 cm for a triangle. So x is more than ? and less than ?. Type both numbers, smaller first.
Zee's triangle of paper strips has sides of 5 cm and 9 cm and a third side that works. Its perimeter is more than ? cm and less than ? cm. Smaller first.
Ari's triangle of pieces of yarn has sides of 3.5 cm and 6 cm and a third side that works. Its perimeter is more than ? cm and less than ? cm. Smaller first.
Esme's triangle of pencils has sides of 4.5 cm and 10 cm and a third side that works. Its perimeter is more than ? cm and less than ? cm. Smaller first.

Can three lengths make a triangle?. Every version has 10 questions, and the answer key prints on the second page.

I can tell whether three lengths make a triangle: the two shorter sides together must be longer than the longest. If they are exactly as long, the shape lies flat.
I can give the range of a third side: more than the difference of the other two, less than their sum.
I can use that range for whole-number sides, isosceles triangles, sides written with x, and the perimeter.

Standard: state-only (related 7.G.A.2)

longest side: The side you compare with: the base in the sketch.

flat: The two sides lie along the base with no corner on top: not a triangle.

difference: The bigger side take away the smaller one.

range: All the lengths between the two ends, without the ends themselves.

isosceles triangle: A triangle with two equal sides.

Your child counted a flat shape as a triangle: when the two shorter sides add to exactly the longest, they lie flat along it.

Your child thought any three lengths make a triangle. Lay two short strips along a long one: if they do not reach past it, there is no triangle.

Your child added the longest side to a short one. That sum is always longer than the other side, so it tells nothing. Add the two shorter sides.

Ask: is there a corner at the top?

What is the most common mistake with can three lengths make a triangle??

Your child counted a flat shape as a triangle: when the two shorter sides add to exactly the longest, they lie flat along it.

How can I help my child with can three lengths make a triangle??

Ask: is there a corner at the top?

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.

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