Question 1113494
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The base is a square of side length x; its area is x^2.<br>
The sides of the tent are four congruent triangles with base x.
The altitude of each triangle is the slant height of the pyramid.
With the square base of side length x and a center pole of 12, the slant height is the hypotenuse of a right triangle with legs x/2 and 12.<br>
So the area of each triangular side of the tent is one-half base times height:
{{{(1/2)(x)(sqrt((x/2)^2+12^2))}}}<br>
The total surface area of the four sides and bottom of the tent is then
{{{x^2+2x(sqrt((x/2)^2+12^2))}}}<br>
This total surface area is to be 864:<br>
{{{x^2+2x(sqrt((x/2)^2+12^2)) = 864}}}
{{{2x(sqrt((x/2)^2+12^2)) = 864-x^2}}}
{{{4x^2(x^2/4+144) = 746496-1728x^2+x^4}}}<br>
(Looks ugly -- but the x^4 terms will cancel, leaving a simple quadratic equation...)<br>
{{{x^4+576x^2 = 746496-1728x^2+x^4}}}
{{{2304x^2 = 746496}}}
{{{x^2 = 324}}}
{{{x = 18}}}<br>
Answer: The side length of the tent is 18 feet.<br>
(by the way... I don't think this is a CAMPING tent!!)