Question

passing through (4,-2) and perpendicular to x=5/4y-2. Write in slope intercept form.

Answer 1

@zepdrix

Answer 2

is the negative 2 also in the denominator? It's a little hard to read correctly without brackets.\[\large x=\frac{5}{4y-2}\]

Answer 3

\[\large x=\frac{5}{4}y-2\]Oh like this? :) That would make more sense lol

Answer 4

no it isn't. it's like the second one you just put up.

Answer 5

Let's first get our line into slope-intercept form, so we can accurately identify the slope. We want it in this form,\[\large y=mx+b\]

\[\large x=\frac{5}{4}y-2\]Start by adding 2 to each side,\[\large x+2=\frac{5}{4}y\]Multiply each side by 4/5,\[\large \frac{4}{5}(x+2)=\left(\frac{5}{4}y\right)\frac{4}{5}\]The fractions will cancel out on the right, giving us,\[\large y=\frac{4}{5}x+\frac{8}{5}\]

So we've got our line in slope-intercept form, this will make it easier to work with. Understand those steps so far?

Answer 6

oh i had put a -4/5

Answer 7

but yes other than that i get it so far

Answer 8

So it looks like our slope \(\large m\) is \(\large \dfrac{4}{5}\).

Do you know what it means for a line to be `perpendicular`?
It relates to the slope. :)

Since the line we're trying to form is perpendicular to this line, it will have a slope that is a `negative reciprocal` of this slope. Do you understand what that means? c:

Answer 9

-4/5 correct? that would be the reciprocal

Answer 10

Hmm I believe it's going to be, -5/4.
Yes the negative looks good. But then we take the reciprocal (the flip) of our fraction.

Answer 11

oh okay

Answer 12

So we're trying to form an equation for a line perpendicular to the given line. Let's call this new line something likeeeee \(\large y_p\).

So we're trying to get an equation for this line, \(\large y_p=mx+b\).
We've determined that the slope is, \(\large m=-\dfrac{5}{4}\).

Now we need to find the \(\large b\) value, the `y-intercept`.
To do so, we'll plug in the coordinate pair they gave us, that this line passes through.

Answer 13

So plug \(\large (4,-2)\) into our equation \(\large y_p=-\dfrac{5}{4}x+b\).

Answer 14

okay

Answer 15

i think im messing up so where

Answer 16

for som reason im getting y=-4/5x+6/5

Answer 17

i mean -5/4x+6/5

Answer 18

So plugging in our point gives us,\[\large -2=-\frac{5}{4}(4)+b\]The 4's will cancel out,\[\large -2=-\frac{5}{\cancel4}(\cancel4)+b\]Giving us,\[\large -2=-5+b\]Adding 5 to each side,\[\large b=3\]
Did you do something different?

Answer 19

yeah i did

Answer 20

i was doing it wrong

Answer 21

so y=4/5x+8/5 is correct?

Answer 22

This was the equation of the line we started with,
\[\large y=\frac{4}{5}x+\frac{8}{5}\]

They gave us a bunch of information to find a different line.
And that was this line,\[\large y_p=mx+b\]
We determined that the slope is \(\large m=-\dfrac{5}{4}\).
And that the y-intercept is \(\large b=3\).

Answer 23

The p doesn't mean anything, you don't need to put that if you don't want. It was just so we could tell it apart from our original y, which referred to a different line.

Answer 24

so the answer is y=-5/4x+3

Answer 25

ya :)