Question

In Exercises 20 and 21 show that points P, Q, and R are collinear by showing that PQ and OR have the same slope.

P(-1, 3) Q(2, 7) R(8, 15)

Short answer

We have proved that the points$P,Q\text{and}R$ are collinear.

Step-by-step solution

Step-1 – Given

The given points are$P\left(-1,3\right),Q\left(2,7\right)\text{and}R\left(8,15\right)$.

Step-2 – To determine

We have to show that points $P,Q\text{and}R$are collinear by showing that$\overline{PQ}$ and$\overline{QR}$ have the same slope.

Step-3 – Calculation 

We’ll use the slope formula:

$m=\frac{y_2-y_1}{x_2-x_1}$

The given points are$P\left(-1,3\right),Q\left(2,7\right)\text{and}R\left(8,15\right)$.

Slope of$\overline{PQ}$:

$\frac{y_2-y_1}{x_2-x_1}=\frac{7-3}{2-\left(-1\right)}=\frac{4}{3}=1.34$

Slope of$\overline{QR}$:

$\frac{y_2-y_1}{x_2-x_1}=\frac{15-7}{8-2}=\frac{8}{6}=1.34$

Since, the slope of $\overline{PQ}$and $\overline{QR}$are equal, so the points$P,Q\text{and}R$ are collinear.