Question

John ordered a large three topping pizza for $7. 50 and a large 8 topping pizza for $10. Write an equation in slope-intercept form to describe the situation. (use fractions) (15 points)

Answer 1

to get the equation of any straight line, we simply need two points off of it, well, let's use the provided values hmmm

$\begin{array}{ccll} \stackrel{toppings}{x}&\stackrel{cost}{y}\\ \cline{1-2} 3 & 7.50\\ 8& 10 \end{array} \qquad\implies \qquad (\stackrel{x_1}{3}~,~\stackrel{y_1}{7.50})\qquad (\stackrel{x_2}{8}~,~\stackrel{y_2}{10}) \\\\\\ \stackrel{slope}{m}\implies \cfrac{\stackrel{rise} {\stackrel{y_2}{10}-\stackrel{y1}{7.50}}}{\underset{run} {\underset{x_2}{8}-\underset{x_1}{3}}}\implies \cfrac{2.5}{5}\implies \cfrac{~~ \frac{25}{10}~~}{5}\implies \cfrac{25}{50}\implies \cfrac{1}{2}$

$\begin{array}{|c|ll} \cline{1-1} \textit{point-slope form}\\ \cline{1-1} \\ y-y_1=m(x-x_1) \\\\ \cline{1-1} \end{array}\implies y-\stackrel{y_1}{7.50}=\stackrel{m}{\cfrac{1}{2}}(x-\stackrel{x_1}{3})\implies y-\cfrac{750}{100}=\cfrac{1}{2}(x-3) \\\\\\ y-\cfrac{15}{2}=\cfrac{1}{2}x-\cfrac{3}{2}\implies y=\cfrac{1}{2}x-\cfrac{3}{2}+\cfrac{15}{2}\implies y=\cfrac{1}{2}x-6$