help with 1 tricky question please :( bit confused! not sure if working is right

[hello_kitty]

Find the value(s) of y so that the distance between the points (5,y) and (8,-1) is 5 units.
Show all working.


What does 5 units mean?


I did...

m = y2 - y1/x2 - x1

5 = -1 - y/8-5
5 = -1 - y/3
15 = -1 -y
16 = -y

I have no idea why i put 5 as m
y = -16

Thnaks!


AND ALSo..
just clarifying...
for a question like:

y -3 = 3/2 (x - 6)
would you expand the bracket first? then multiply the two to the LHS? OR multiply the 2 to the left hand side so it is
2(y - 3) = 3(x-6)?

I tried both ways and got differenet answers :/
could i see both ways workings?


thanks a lot!

[JinXi]

m is the gradient.

the distance is 5 units, not the gradient.

Try using the Pythagoreas Theorem.

You should get y= -5, y=3

[Greatness]

Use the distance formula and rearrange, to make y the subject.
distance=square root ((x1-x2)^2 + (y1-y2)^2)

There may be an easier way to do this. Not quite sure, that was the first method that i thought of.

[simonhu81292]

for your first question ... m does not equal 5...
you are using the wrong formula as well
they are asking for the distance...
hence .. you should now use this formula
Root[(x2-x1)^2+(y2-y1)^2] ..
now you can try and solve it ...

[simonhu81292]

for your second question...
both approach will still work
however ...using your first methods would be faster
y -3 = 3/2 (x - 6)
you would expand the RHS, then move the 3 to the RHS by +3

[hello_kitty]

Im a bit stuck when i get to

5 = square root (8-5)^2 + (-1-y)^2

:/

[ttn]

square both sides

[simonhu81292]

first get this bit (8-5)^2 , which equals 9
then square both sides ..
you would get 25=9+(-y-1)^2
then you move the 9 on to the LHS
16=(-y-1)^2
expand (-y-1)^2
16=y^2+2y+1
bring the 16 onto the RHS
y^2+2y-15=0
solve for y
and then you will get y= -5 or 3 as your answer

[ttn]

Or instead of expanding, you can just square root both sides

(plus/minus 4)

[hello_kitty]

so the answer can be either 3 or -5??

[simonhu81292]

Or instead of expanding, you can just square root both sides

(plus/minus 4)

lol...didn't think of it that way ..yeah ~~
faster~

so the answer can be either 3 or -5??

yep ..that's right  =hello_kitty link=topic=38126.msg403523#msg403523 date=1297678750]
so the answer can be either 3 or -5??
[/quote]
yep ..that's right

[luffy]

Honestly, I don't think you are getting anything out of this thread, even though you now know the answer.
Do you actually understand how to do the question?

If not, members of this thread have already told you how to do the question, the only way in which you will understand it properly, is if there is a teacher or someone showing you how to do it face to face, with visual representations.

Tell me if I am wrong because teaching you how to do this question (without you understanding), will not actually teach you how to do these 'type' of questions, if you get what I mean.

[hello_kitty]

i do get it..

25 = 10 +y^2 +2y
15 = y^2 + 2y
y^2 + 2y - 15 = 0

(y + 5) y - 3) = 0

therefore, y = -5 or y = 3.


yeah.. i get it

[luffy]

i do get it..

25 = 10 +y^2 +2y
15 = y^2 + 2y
y^2 + 2y - 15 = 0

(y + 5) y - 3) = 0

therefore, y = -5 or y = 3.


yeah.. i get it

Haha ok. My bad then.

[hello_kitty]

Its alright
I just forgot what the method was for..


y2 + 2y - 15 = 0 to (y +5) (y-3) = 0

:/