The missing coordinate r is 11.
Solution:
Given points are (–15, 1) and (–7, r).
[tex]x_{1}=-15, x_{2}=-7, y_{1}=1 \text { and } y_{2}=7[/tex]
Slope (m) = [tex]\frac{5}{4}[/tex]
To find the missing coordinate r:
Slope formula:
[tex]$m=\frac{y_{2}-y_{1}}{x_{2}-x_{1}}$[/tex]
Substitute the given values in the formula.
[tex]$\frac{5}{4}=\frac{r-1}{-7-(-15)}[/tex]
[tex]$\frac{5}{4}=\frac{r-1}{-7+15}[/tex]
[tex]$\frac{5}{4}=\frac{r-1}{8}[/tex]
Do cross multiplication.
[tex]8 \times 5=4(r-1)[/tex]
40 = 4r – 4
Add 4 on both side of the equation.
44 = 4r
Divide by 4 on both side of the equation.
11 = r
⇒ r = 11
Hence the missing coordinate r is 11.
