Question 86097
This is a Pythagorean theorem problem. The Pythagorean theorem says that the sum of the squares
of the two legs of a right triangle is equal to the square of the hypotenuse of the triangle.
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In equation form this becomes:
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{{{a^2 + b^2 = c^2}}}
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in which "a" and "b" are the legs of the right triangle, and "c" is the longest side which
is also called the hypotenuse.
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Just substitute the two values for the legs that you are given into this equation. Since you
are told that one leg is 6 ft let's call that length "a". Then length "b" will be the other
leg or 8 ft. When you substitute these values, the equation becomes:
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{{{6^2 + 8^2 = c^2}}}
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Square both terms on the left side and you get:
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{{{36 + 64 = c^2}}}
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Then add the two values on the left side:
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{{{100 = c^2}}}
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Finally, solve for the hypotenuse by taking the square root of both sides to find that:
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{{{c = sqrt(100) = 10}}}
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Now you know the lengths of all three sides of the garden. To fence in the garden she
will need an amount of fencing equal to the sum of the three lengths.  Therefore, 
she will need:
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{{{6 + 8 + 10 = 24}}}
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So she needs 24 feet of fencing.
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Hope this helps you to understand how the Pythagorean theorem works.