Posted by **ali** on Sunday, September 7, 2008 at 5:44pm.

How do you find an equation of a line perpendicular to y=x at the point (5,5) in standard form?

- Trig -
**Damon**, Sunday, September 7, 2008 at 5:49pm
put the original equation in the form

y = m x + b

in this case

y = 1 x + 0

so m, the original slope, = 1

Now m' = -1/m

so our new slope = -1/1 = -1

so our new function looks like

y = -1 x + b

we need b

use the point

5 = -5 + b

b = 10

so

y = -x + 10

- Trig -
**drwls**, Sunday, September 7, 2008 at 5:50pm
The slope of y = x is 1, so the slope of a perpendicular line must be -1. (This is becasue the product of the slopes must be -1).

The equation can therefore be written

(y-5)/(x-5) = -1

y-5 = -x +5

y = -x +10

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