Using the vertex of a quadratic equation, it is found that P is at a maximum for l = -0.5 thousand foot-candles.
A quadratic equation is modeled by:
[tex]y = ax^2 + bx + c[/tex]
The vertex is given by:
[tex](x_v, y_v)[/tex]
In which:
[tex]x_v = -\frac{b}{2a}[/tex]
[tex]y_v = -\frac{b^2 - 4ac}{4a}[/tex]
Considering the coefficient a, we have that:
In this problem, the function for P is given by:
[tex]P(l) = \frac{110l}{l^2 + l + 4}[/tex]
The function will be at a maximum when the denominator is at a minimum. The denominator is a quadratic function with coefficients a = 1, b = 1, c = 4, hence:
[tex]l_v = -\frac{b}{2a} = -\frac{1}{2} = -0.5[/tex]
P is at a maximum for l = -0.5 thousand foot-candles.
More can be learned about the vertex of a quadratic equation at https://brainly.com/question/24737967
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