A Difficult Equation

1. Jul 10, 2004

Poweranimals

Perpendicular to y = -1/4x - 12 passing through (3, -4).

2. Jul 11, 2004

Math Is Hard

Staff Emeritus
Hint: If two lines are perpendicular, what does this tell you about their slopes?

3. Jul 11, 2004

Poweranimals

They intersect?

4. Jul 11, 2004

Math Is Hard

Staff Emeritus
well, the lines intersect, yes. but you know what the slope of the first line is, right? your equation is in y =mx+b format so you can tell just by looking.

the slope of the second line will be the opposite reciprocal of the first slope.

5. Jul 11, 2004

NSX

opposite reciprocal?

:P

I prefer to use the term negative reciprocal.

6. Jul 11, 2004

Math Is Hard

Staff Emeritus
I grew fond of "opposite" because there's no confusion if you are talking about the slope of a line that's perp to a line with a negative slope. but that's just me!

7. Jul 11, 2004

Math Is Hard

Staff Emeritus
anyhoo, power animals, what we're saying is that if a line has a slope of positive 3, for example, then the slope of a line that is perpendicular to it would be -1/3.

8. Jul 11, 2004

Math Is Hard

Staff Emeritus
so if the slope of a line is -1/4, then the slope of a line that is perpendicular to it would be...?

9. Jul 11, 2004

gazzo

or when you multiply both slopes together you get -1 ?

my maths teacher had a strange way of explaining things...

10. Jul 12, 2004

abertram28

yes. when multiplied together they will equal -1

so you can see it by setting -1=m1*m2 where m1 or m2 to -1/4.

do you need help finding the whole equation based on that slope and point? you can just plug an x and a y into the y=mx+b way and solve for b too.

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