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The second famous Pythagorean triple after (3,4,5) with 3^2 + 4^2 = 5^2
is (5,12,13) with 5^2 + 12^2 = 25 + 144 = 169 = 13^2.
So, your triangle is (5,12,13) inches. ANSWER
Alternatively, you can solve this quadratic equation
x^2 + (x-7)^2 = 13.
You will get the same triangle, then.
After doing some work, of course.
Solved.