Question 1161035
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You should know how to solve problems like this using the formula for finding the slope of the line containing two given points, as shown by the other tutor.<br>
However, beginning students especially often get wrong answers because they plug the numbers in the wrong places in the formula.<br>
I always encourage students to learn to be able to solve this kind of problem using the basic definition of slope instead of the formula.<br>
Slope is the ratio "rise/run" -- the ratio of how far you move up or down compared to how far you move right or left.<br>
Between the two given points A(x,-7) and B(1,2), we don't now the run (difference in x coordinates), but we know the difference in the y coordinates from A to B is from -7 to +2, which is 9.<br>
Since we are given that the slope is 3, we know that change of 9 in the y coordinate is 3 times the change in the x coordinate -- so the change in the x coordinate is 9/3 = 3.<br>
B has an x coordinate of 1; the x coordinate of A has to be 3 less than that, which is 1-3 = -2.<br>
ANSWER: x = -2<br>