Math CentralQuandaries & Queries


Question from Daryl, a student:

I have a right-angled triangle. two of its sides are 12.6cm. The third/last line is missing. How can I find the length of the last line?

Hi Daryl.

Use the Pythagorean Theorem to find the length. Call the length of the hypotenuse (that's the side opposite the right angle) h and call the length of the two legs (the other sides) a and b. When you do this, the Pythagorean Theorem gives this relationship:

h2 = a2 + b2

Since h, a and b are all larger than zero, you can see from the expression above that h is larger than both a and b. Thus both a and b are 12.6 and you can find h quickly with this and then you can add up the sides to get the perimeter.

Stephen La Rocque and Penny Nom

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