Question

PLEASE HELP ME
How did they get the answers for number 20???

Answer 1

check the picture below, that's the suspension bridge with supporting cables and traffic on it.


`\bf \textit{ vertex of a vertical parabola, using coefficients}\\\\ \begin{array}{lccclll} y = &{{ 0.1}}x^2&{{ -7}}x&{{ +150}}\\ &\uparrow &\uparrow &\uparrow \\ &a&b&c \end{array}\qquad \left(-\cfrac{{{ b}}}{2{{ a}}}\quad ,\quad {{ c}}-\cfrac{{{ b}}^2}{4{{ a}}}\right)`


`\bf \left(-\cfrac{(-7)}{2(0.1)}~~,~~150-\cfrac{(-7)^2}{4(0.1)} \right)\implies \left( \cfrac{7}{0.2}~~,~~150-\cfrac{49}{0.4} \right) \\\\\\ \left( 35~~,~~ 150-122.5\right)\implies (\stackrel{\textit{away from tower}}{35}~~,~~\stackrel{\textit{closest to road}}{27.5})`