State if each set of three numbers can be the lengths of the sides of a triangle and explain why and how you got the answer.
13, 12, 26 i wanted shapes

To find if three number are a triangle, the formula is A^2 + B^2 = C^2. This means that when you square the lowest two terms they need to add to the square of the third number. 
12^2 = 144
13^2 = 169
144 + 169 = 313
26^2 = 676

Since 313 does not equal 676 these numbers cant be the sides of a triangle.

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Where are the calculations?