They create an Acute triangle.
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Explanation: Use the Triangle Inequality Theorem to see if your lengths even make a triangle.
Our sides are 28, 45 and 53.
28 + 45 = 73
73 > 53 Because 73 is greater, we have an actual triangle and can use the Pythagorean Theorem to classify your triangle.
Now we use the Pythagorean Theorem.
a^2 + b^2 = c^2
53 + 28 = 45
53 squared is 7.28. 28 squared is 5.29. 45 squared is 6.7.
Add 5.29 to 6.7 you get 11.99.
11.99 is a greater number than 7.28 so therefore the triangle is acute.
Hope this helped. :)