| If two lines cross and make 90 degree angles between them | ||
| they are called "perpendicular" to each other ... | ||
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| There is an easy test to see if two equation lines | ||
| form 90 degree angles where they cross. | ||
| If they do, then ... | ||
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(slope of one line) x (slope of the other line) = -1 |
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| Example: | ||
| Find out if the graph lines of the equations ... | ||
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3X - 5Y = 7 and 6Y = -10X + 5 |
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| are perpendicular. | ||
| An easy way to find the slope of an equation | ||
| is to make the equation look like ... | ||
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Y = (some number)X + (some other number) |
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| So if you have an equation like ... | ||
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3X - 5Y = 7 |
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| move it around until it looks like Y = (stuff). | ||
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| So the slope of this equation line is 3/5. | ||
| The line goes up from left to right. | ||
| Now let's deal with 6Y = -10X + 5 ... | ||
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| So the slope of this equation line is -10/6. | ||
| That simplifies to -5/3. | ||
| Now we can multiply the two slopes together, | ||
| and see what we get ... | ||
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| When we multiply these slopes together we get -1. | ||
| That means the two equation lines are perpendicular. | ||
| Thrilling, isn't it ... | ||
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copyright 2005 Bruce Kirkpatrick |
