Answer: w = 13 m, L = 19.5 m
Step-by-step explanation:
P = 3w + 2L
3w + 2L = 78
2L = 78 - 3w
[tex]L=\dfrac{78-3w}{2}[/tex]
A = w · L
[tex]A=w\bigg(\dfrac{78-3w}{2}\bigg)\\\\\\A=\bigg(\dfrac{78w-3w^2}{2}\bigg)\\\\\\A=39w-\dfrac{3}{2}w^2\\\\\\0=-\dfrac{3}{2}w^2+39w-A[/tex]
a=-3/2 b=39
[tex]\text{Axis of Symmetry}:w=\dfrac{-b}{2a}=\dfrac{-39}{2(-\frac{3}{2})}=\dfrac{-39}{-3}=\large\boxed{13}[/tex]
[tex]\text{Maximum}:L=\dfrac{78-3w}{2}=\dfrac{78-3(13)}{2}=\dfrac{78-39}{2}=\dfrac{39}{2}=\large\boxed{19.5}[/tex]
