VIDEO: Calculate missing coordinate

How to calculate the missing x value

The general straight line equation is f (x) = mx + n. In order to be able to calculate the missing x-coordinate, you of course first need your straight line equation and the y-value.

1. Plug the y-value into your straight line equation as f (x).
2. Subtract n on both sides of the straight line equation.
3. Now divide both sides of the equation by m. So in general you get x = (f (x) - n): m and thus the missing x-coordinate.
4. Example: You have given the function f (x) = 2x - 3 and the y-value y = 5. Substituting 5 for f (x), you get the equation 5 = 2x - 3. Now subtract (-3). This means that you add 3 on both sides of the equation: 5 + 3 = 2x - 3 + 3. Simplified, this gives the equation 8 = 2x. If you divide the entire equation by m, i.e. 2 here, you get 8: 2 = 2x: 2 and thus 4 = x. With the missing x-coordinate you get the point P (4/5).


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How to calculate the y-coordinate

The general straight line equation is also here f (x) = mx + n. However, you have now given the x-coordinate and you have to calculate the corresponding y-value.

1. Substitute x into the straight line equation. Calculate the function normally by first multiplying x by m and then adding n to the result.
2. The obtained value f (x) corresponds to your y-coordinate. So you have the point P (x / f (x)).
3. Example: Your function is f (x) = 2x - 3 and your x value is 5. If you plug x into the straight line equation, you get f (5) = 2 * 5 - 3. By simple calculation you get f (5) = 10 - 3 and thus f (5) = 7. The point is therefore P (5/7).