You can put this solution on YOUR website! the slope of a line is -2 and the line contains the points (7 4) and (x 12) what is the value of x?
:
We can use the slope equation: m =
where:
x1 = 7; y1 = 4
x2 = x; y2 = 12
m = -2
:
-2 =
-2(x-7) = 8
-2x + 14 = 8
-2x = 8 - 14
-2x = -6
x = -6/-2
x = +3
:
:
Check = = -2
Of course you should know how to find the answer to the question using the slope formula.
But I have seen far too many cases where a student either doesn't understand the formula or gets the wrong numbers in the wrong places, ending up with a wrong answer.
I encourage students to be able to solve a problem like this using an UNDERSTANDING of what slope is.
For this problem, you might do something like this....
(1) The slope is negative, so the graph is downhill to the right.
(2) Since the two y values are 4 and 12 and the slope is negative, the point with y=12 is farther to the left.
(3) The difference between the two y values is 8; since the slope is -2, the difference between the two x values must be 4.
(4) So (x,12) is 4 units to the left of (7,4), making x equal to 3.
