Graphing linear equations — Harder example | Math | SAT | Khan Academy

Watch Sal find a point on a perpendicular line in the xy-plane.

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[lyliah]

I didint understand the part why he take the negative of 1/3,

[shannenlibres]

1:38 why is g times 1 equal to negative five? How did you know g is -5?

[riaraghu]

Thanks so much but you could explain at a more basic level...

[TasyaAdzkiya]

3:00 The slope, in that case, means that for every negative 3 steps of y, there is positive one step of x. Let's say the -3 (the difference or the "distance" between two x-points we know) is a "package" of one step of x. To know the corresponding y (g of -2) value, we should find the difference or "distance" of the two y-points, even though we haven't find one of the y-value, by using the pattern from the slope.

We multiply the "package" of one step of x (in this case, we consider the -3 difference between two x-points as a "package" of one step of x) by -3 because the slope is -3/1 or -3, which means for every negative three steps of y, there is positive one step of x because the formula for slope is the change is y over the change in x. So, -3 × -3 = 9. That is the difference between two y-points that we know. From that, we can find the other y-point, which is g(-2).

[frank-mxib]

im confused with him putting minus two in the end, can someone explain?