Question

find k so that the line through 4,k and 2,-1 is perpendicular to y=2/5x-3

Answer 1

the slope of the line is -5. rise/run=-5
(k+1)/(4-2)=-5
solve for k

Answer 2

i mean -5/2 is the slope

Answer 3

do you know how to finish the problem?

Answer 4

no.

Answer 5

\[\frac{-5}{2}=\frac{k+1}{4-2}\]now "cross multiply" this clears the 2 from the denominator\[-5=k+1\]subtract 1 to find k\[-6=k\]

Answer 6

no you did it wrong.....shouldn't it be y2-y1 instead of y1-y2

Answer 7

so instead of k+1 at the top it should be -1-k

Answer 8

the slope of the given line is 2/5
the slope of the required line is -5/2
so the line must be in the form ,y=(-5/2)x+C,where C is some constant
now apply the given points, (2,-1) we get, -1=(-5/2) (2)+C
=>C=4
so the required line equation is y=(-5/2)x+4
now apply the other point ,(4,k)=>k=(-5/2)4+4
=>k=-10+4
=>k=-6

Answer 9

what if the points were written (2,-1) and (4,k)? would k then be y2?

Answer 10

yeah, but it's written as 4,k and 2,-1...therfore -1 is y2 and u start with it.

Answer 11

not so, what matters in the approach that colton started, is that you remain consistent with respect to the position of coordinates when you set-up the slope formula. Simply because one point is written to the left of another in the problem does not make it point1 or point 2, that is you choice. I chose the set that gave the fewest number of negative signs

Answer 12

but shouldnt we then get the same answer

Answer 13

is went right to left and i got -12

Answer 14

i**

Answer 15

That said, if you set it up and did it according to \[\frac{-5}{2}=\frac{-1-y}{2-4}\]you would get the same result.

Answer 16

i did that, then i got -10=-k-2

Answer 17

-10+20 i mean

Answer 18

you forgot to divide by 2 of the LHS; the LHS should be -5 not -10, then it works out

Answer 19

???

Answer 20

lhs?

Answer 21

LHS=left hand side

Answer 22

dont u cross multiply and dont have to divide?

Answer 23

lets see, if we cross multiply we get\[-2*(-5)=2(-1-k)\]\[10=-2-2k\]\[12=-2k\]\[-6=k\]

Answer 24

you forgot +20 in the first step and completely ignored the -4

Answer 25

it's 2-4

Answer 26

also go see dashni's solution; you might like that method better

Answer 27

2-4 in the right side denominator is -2; then you see the negative mutliplying the -5 on the right side after the cross mult.

Answer 28

i dont get why u just ignmored the -4 though

Answer 29

i didn't ignore the -4; i simplified 2-4=-2!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Answer 30

ohhhhhhhhhhhhhhhhhhhhhhhh

Answer 31

WOW THAT MAKES SENSE NOW

Answer 32

there were a few responses between the start and restart of that way; I should have started from the beginning; btw, go see dashni's solution to the problem-- you might find it more to your liking

Answer 33

no i didnt get tht...urs was better.

Answer 34

actually it was colton's to start

Answer 35

in other news....have u read the hunger games?

Answer 36

I might check it out, thanks!