Question

Find the equation of the line, given the following information:

Passes through (-9,3) and is perpendicular to y =1/2x+6.

Answer 1

y = -2x - 15

Explanation:

We are given 2 pieces of information: (1) a point our line passes through, and (2) a line it is perpendicular to. The only thing we need from (2) is the slope.

We know that perpendicular lines have opposite signs and are inverses (denominator and numerator switched). So our line must have a slope of

m = -2

Using our equation for a line: y = mx+b, our line so far is

(I) y = -2x + b

Let's use the point we have (-9,3) and substitute what we know into equation (I) to find b.

x = -9

y = 3

(I) (3) = -2(-9) + b

3 = 18+b

b= -15

Now we have m and b so we can write the equation of our line:

y = -2x - 15