Question 231846
Draw the picture.
The point where the wire touches the ground divides 
the base into two parts: x and 10-x
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You have two right triangles and the wire forms the hypotenuse of 
both of those triangles.
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Hypotenuse 1 = sqrt(6^2 + (10-x)^2)
Hypotenuse 2 = sqrt(8^2 + x^2)
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Equation:
sqrt(36 + (10-x)^2) + sqrt(64 + x^2) = 18
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Solve for "x" to find the point where the wire should touch the ground.
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Cheers,
Stan H.