maths help asap :( please

[elerrina]

i've been trying to do this maths question but i cant get the right answer. the question is find the gradient of the line which passes through (4,3) and is parallel to y=3x+5
I've followed the steps the maths teacher gave us and still cant arrive at the right answer which is y=3x+9 if anyone could help and right out what they did i would be immensely great full. thanks

[babybombo]

http://www.bbc.co.uk/scotland/education/bitesi ze/higher/maths/geometry/index.shtml

Use this link then click on straight line> revise

It is from the scottish site but maths is the same in every country =)
Hope this helps, this is the topis Im doing in class right now, I tried your question but didnt have any luck so maby this will help !

[elerrina]

i took a look at that but its really different to the method we were taught and slightly confusing :/ any other suggestions would be great

[Buenchico]

Either your maths teacher has got it wrong(!) or you've copied the answer incorrectly. (Actually, you seem to have copied the question incorrectly as well. You appear to be seeking an equation, not a gradient, as the answer to your problem).

The graph of y = mx +c always has a gradient equal to m (and a y-intercept equal to c). So y = 3x + 5 must have a gradient of 3.

Since the required line is parallel to y = 3x + 5, it must also have a gradient of 3.
i.e. the required line is of the form y = 3x + c

All we need to do is to find the value of c. We know that the line passes through (4,3) so we know that when x = 4, y =3. So let's put those values into y = 3x + c:
We get 3 = (3x4) +c
<=> 3 = 12 + c
<=> c = -9

Putting that into y = 3x + c gives us
y = 3x - 9

Chris
(Maths graduate with 15 years teaching experience - so I hope I've got it right!)