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# finding the equation of a perpendicular line watch

1. Ok, so I fixed the quadratics to get this:

which meant that x was equal to 2 and 1/2.

Which equation do I substitute the (I assume) 1/2 into?
2. (Original post by frostyy)
Ok, so I fixed the quadratics to get this:

which meant that x was equal to 2 and 1/2.

Which equation do I substitute the (I assume) 1/2 into?
You can substitute them into either equation and they will return the same y value (after all, the points appear on both lines). You've got x=0.5 and x=2. What does this mean? Well, it means you've got your x coordinates for points A and B respectively. To find the y coordinates you just plug these values back in (doesn't matter which equation as the answer should be the same). You should then get a pair of answers.

When x = 2, y = ?
When x = 0.5, y = ?

Well, we know that point B is (2,8) because you wrote that down already in the original picture. We can confirm this by substitution. Recall that the equations of the lines are and . Now for the check: and . So (2,8) is a point that appears on both lines indeed. Now you need to find the y coordinate when x = 0.5. And remember, it doesn't matter which equation you substitute that into because the answer should be the same.

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