Answer:
The length of the pool is [tex]L=24\:ft[/tex].
Step-by-step explanation:
The area of a rectangle is given by [tex]A=L\cdot W[/tex] where L is the length, W is the width.
If the length of the pool is 9 feet more than it’s width, this means that [tex]L=9+W[/tex]
We know that the area of a rectangular swimming pool is 360 [tex]\:ft^2[/tex]. So we simple insert the length ([tex]L=9+W[/tex]), width ( [tex]W[/tex]) and area (360) into the formula and solve the resulting equation.
[tex]360=\left(9+W\right)W\\\\360=9W+W^2\\\\9W+W^2=360\\\\W^2+9W-360=0[/tex]
[tex]\mathrm{Solve\:with\:the\:quadratic\:formula}\\\\\mathrm{For\:a\:quadratic\:equation\:of\:the\:form\:}ax^2+bx+c=0\mathrm{\:the\:solutions\:are\:}\\\\x_{1,\:2}=\frac{-b\pm \sqrt{b^2-4ac}}{2a}[/tex][tex]\mathrm{For\:}\quad a=1,\:b=9,\:c=-360:\quad W_{1,\:2}=\frac{-9\pm \sqrt{9^2-4\cdot \:1\left(-360\right)}}{2\cdot \:1}\\\\W=\frac{-9+\sqrt{9^2-4\cdot \:1\left(-360\right)}}{2\cdot \:1}= 15[/tex]
[tex]W=\frac{-9-\sqrt{9^2-4\cdot \:1\left(-360\right)}}{2\cdot \:1}= -24[/tex]
A length cannot be negative. So [tex]W=15[/tex] and the length of the pool is [tex]L=9+15=24\:ft[/tex]
