Question

A line has a y intercept of 8 and a slope of -2. What is the equation of a line that is perpendicular to this line.?

Select one:
O A. y=-1/2x+8
O B. y = 2x + 8
C. y= 1/2x+4
OD.y=-2x+4

Answer 1

Y=1/2x+4
Slopes a.a’=-1

Answer 2

Use the equation of a line: y = mx + c
- “M” stands for the slope
- “C” is the coordinate “y” when the line intercepts the y axis.

Any line which is perpendicular to another has the opposite gradient/slope of the original line: instead of 2, we now have 1/2. Easy way to do this is simply give it the reverse sign (+ or -) and flip the numerator and denominator.

Therefore, we replaced m with 1/2.

Usually to find c and therefore complete the equation, we need a coordinate which the line crosses, to which we substitute its values into y and x and solve for c.

Since we aren’t given that though, we can just do factor of elimination, giving C) as your answer because it is the only one with the gradient which we found.