A city planner is rerouting traffic in order to work on a stretch of road. The equation of the path of the old route can be described as y = two fifthsx − 4. What should the equation of the new route be if it is to be perpendicular to the old route and will go through point (Q, P)?

y − Q = negative five halves(x − P)
y − Q = two fifths(x − P)
y − P = negative five halves(x − Q)
y − P = two fifths(x − Q)

1 answer

To find the equation of a new route that is perpendicular to the old route, we first need to determine the slope of the old route. The old route is given by the equation:

\[ y = \frac{2}{5}x - 4 \]

From this equation, we can see that the slope (m) of the old route is \( \frac{2}{5} \).

To find the slope of the new route, which is perpendicular to the old route, we use the fact that the product of the slopes of two perpendicular lines is -1. If the slope of the old route is \( m_1 = \frac{2}{5} \), then the slope of the new route \( m_2 \) is:

\[ m_2 = -\frac{1}{m_1} = -\frac{1}{\frac{2}{5}} = -\frac{5}{2} \]

Now we have the slope of the new route as \( -\frac{5}{2} \).

We can then use the point-slope form of the equation of a line, which is given by:

\[ y - y_1 = m(x - x_1) \]

where \( (x_1, y_1) \) is a point on the line (in this case, it is point (P, Q)), and \( m \) is the slope. Substituting in \( m = -\frac{5}{2} \) and the point \( (P, Q) \), we have:

\[ y - Q = -\frac{5}{2}(x - P) \]

Thus, the correct equation for the new route, which is perpendicular to the old route and goes through the point (P, Q), is:

\[ y - Q = -\frac{5}{2}(x - P) \]

This corresponds to the first option provided:

y − Q = negative five halves(x − P)