Question

Write an equation in point-slope form, y – y1 = m(x – x1), of the line through points (9, –2) and (10, 2). Use (9, –2) as the point (x1, y1).

Answer 1

$\bf \begin{array}{ccccccccc} &&x_1&&y_1&&x_2&&y_2\\ % (a,b) &&(~ 9 &,& -2~) % (c,d) &&(~ 10 &,& 2~) \end{array} \\\\\\ % slope = m slope = m\implies \cfrac{\stackrel{rise}{ y_2- y_1}}{\stackrel{run}{ x_2- x_1}}\implies \cfrac{2-(-2)}{10-9}\implies \cfrac{2+2}{10-9}\implies \cfrac{4}{1}\implies 4 \\\\\\ % point-slope intercept \stackrel{\textit{point-slope form}}{y- y_1= m(x- x_1)}\implies y-(-2)=4(x-9)\implies y+2=4(x-9)$