Once you know the slope (m), you're halfway there. Now all that's left to find is the y-intercept (b). To find the y-intercept, choose one of the points on the line. It does not matter which point you choose (just pick the one that looks easiest to you). Plug in the values for x and y into the equation and solve for b.
At this point, you've solved for both m and b. All that's left to do is to plug them both in and write the equation in slope-intercept form (y = mx + b).
It's always a good idea to check your work when possible. To double check the accuracy of your equation, you can use the other point that's on the line (the one you didn't use in Step 2 to find b). Plug in the x value from this point into your y = mx + b equation and see if it comes out to the correct y value.
Step 1: Find the slope (m).
Once you know the slope, plug it in for m in y = mx + b. This gives you y = 3x + b.
Pick one of the points on the line and use the x and y values to find b. It does not matter which point you choose. We'll pick the first point (4,7) and plug in 4 for x and 7 for y.
We used the point (4,7) in Step 2, so to check our equation we need to use the other point: (6,13). If you use the same point twice, it will not find a mistake. Make sure to use the point you didn't use to find the y-intercept in Step 2. Plug in the x value from the other point and see if it works. If we plug in 6 for x in our equation, the y value should come out to 13. 3(6) - 5 = 18 - 5 = 13. It works!If we had plugged in 6 and it came out to a number that wasn't 13, that would tell us that we had made a mistake somewhere along the way. If this happens to you, start by double checking to make sure you calculated the slope correctly. You may have used the formula incorrectly or missed a negative sign somewhere. Ready to try a few problems on your own? Click the START button below to try a practice quiz!
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