Line Perpendicular A002A8
1. **Problem statement:** Given points $P(-4,2)$ and $Q(5,-4)$, a line $l$ is drawn through $P$ and perpendicular to the line segment $PQ$. This line $l$ meets the $y$-axis at point $R$. We need to find:
a. The equation of line $l$
b. The coordinates of point $R$
c. The area of triangle $PQR$
2. **Find the slope of line $PQ$:**
The slope formula is $m = \frac{y_2 - y_1}{x_2 - x_1}$.
For $P(-4,2)$ and $Q(5,-4)$:
$$m_{PQ} = \frac{-4 - 2}{5 - (-4)} = \frac{-6}{9} = -\frac{2}{3}$$
3. **Find the slope of line $l$ (perpendicular to $PQ$):**
The slope of a line perpendicular to another with slope $m$ is the negative reciprocal, so:
$$m_l = -\frac{1}{m_{PQ}} = -\frac{1}{-\frac{2}{3}} = \frac{3}{2}$$
4. **Find the equation of line $l$ passing through $P(-4,2)$ with slope $\frac{3}{2}$:**
Use point-slope form:
$$y - y_1 = m(x - x_1)$$
$$y - 2 = \frac{3}{2}(x + 4)$$
Simplify:
$$y - 2 = \frac{3}{2}x + 6$$
$$y = \frac{3}{2}x + 8$$
This is the equation of line $l$.
5. **Find the coordinates of point $R$ where line $l$ meets the $y$-axis:**
On the $y$-axis, $x=0$, so substitute $x=0$ into the equation of $l$:
$$y = \frac{3}{2}(0) + 8 = 8$$
Thus, $R = (0,8)$.
6. **Find the area of triangle $PQR$:**
The vertices are $P(-4,2)$, $Q(5,-4)$, and $R(0,8)$.
Use the formula for the area of a triangle given coordinates:
$$\text{Area} = \frac{1}{2} \left| x_1(y_2 - y_3) + x_2(y_3 - y_1) + x_3(y_1 - y_2) \right|$$
Substitute:
$$= \frac{1}{2} | -4(-4 - 8) + 5(8 - 2) + 0(2 + 4) |$$
$$= \frac{1}{2} | -4(-12) + 5(6) + 0 |$$
$$= \frac{1}{2} | 48 + 30 | = \frac{1}{2} \times 78 = 39$$
**Final answers:**
a. Equation of line $l$: $y = \frac{3}{2}x + 8$
b. Coordinates of $R$: $(0,8)$
c. Area of triangle $PQR$: $39$ square units