



 
Hi, I think you missed one word in this question. Since one side of the triangle is its hypotenuse the triangle must be a right triangle. Since the angle between the base and the third side is a right angle. the length of the third side is the height of the triangle. Suppose this length is $x$ units, the length of the base is $b$ units and the length of the hypotenuse is $h$ units. Pythagoras Theorem then tells us that \[x^2 + b^2 = h^{2}.\] hence \[x = \sqrt{h^2  b^2} \mbox{ units.}\] Penny 



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