Maths Question

[jodyemm]

ABCD is a parallelogram. A, B and C have coordinates (2,3) , (4,7) and (8,11). Find the equation of DC

[sith123]

its hard to do this without a diagram lol...that and i got an f in maths when i was younger :)

[Calibax]

You should plot the three known points on graph paper and it will become obvious where the fourth point of a parallelogram should be.
Knowing the 2 points D & C;
The line through two distinct points (x1, y1) and (x2, y2) is given by

y = y1 + [(y2 - y1) / (x2 - x1)]·(x - x1)

[sith123]

what he said lol

[jake-the-peg]

DC is parallel to AB - it's a parallelogram as it's parallel it will have the same gradient as AB you can work out the gradient by the difference in the y cor-ordinates divided by the difference in the x co-ordinates can't you?

That gives you the m in y=mx+c

now you just neet the y intercept for the c

you know the point C is on DC so you know values for x and y and you have m from step 1 so you can find c

[factor-fiction]

Did these answers help, jodyemm?

[stymied]

A simple diagram should give immediately D as (6,7). Reason: BC and AD are parallel and B->C is 4 across (increase in x) and 4 up (increase in y) gives D as
(2+4,3+4) (ie. 4 across and 4 up from A) =(6,7). The equation of DC should now be easy.