How do you do Test 9 section 3 number 20?

This question is about perpendicular lines, so the first thing to remember is that perpendicular lines have negative reciprocal slopes. The graph of , shown, has a slope of -2. That means the slope of , *not* shown, must have a slope of .

The second thing to quickly note is that this question is using function notation and asking for . That’s the same as asking for the -intercept; it’s just the question 20 way to ask it.

We know that passes through , and we know it has a slope of , so all we really need to do is count leftwards. is only 1 unit away from the -axis, and when you have a slope of , you travel 0.5 units down when you travel 1 unit left. Therefore, the -intercept—aka —is 2.5.

If you like algebra better, you can plug the slope and the point you know into slope-intercept form () and solve for :