Question

Need some help.

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Answer 1

@mathmate

Answer 2

Apply Pythagoras Theorem,
Hypotenuse ^2 = c^2 = a^2+b^2
Here the two known sides are a=4, b=5.
So calculate c (hypotenuse) using the above formula.
Use your calculator, and don't forget to calculate the square-root of c^2.