3 replies to this topic

[xClairex]

aah i have just realised hw much i cant do unit 1

i cant do these questions which are probz straight 4ward but i cant do them

for some reason my diagram isn't uploading

in the diagram A is the point (7,0), B is (-3,-2 and C (-1,8)
The median CE and the altitude BD intersect at J.

a)find the equations of CE and BD

b)find the co-ordinates of J.


so far i have

mAB= [0-(-2)] / [7-(-3)] = (0 + 2) / (7 + 3) = 2/10 = 1/5 therefore mAB = 5/1 = 5 since m1 * m2 = -1

using c = (-1,8) in y - y1 = m (x-x1)
gives y-8=-1 (x-(-1))
y-8=-1(x+1)
y-8=-x - 1
y=-x -1 + 8
y=-x + 7
therfore y + x = 7

can anyone tell me what to do next and if that is right or wrong? thank you in advance

[Dave]

you have gotten a little confused

median is the middle point of the line AB but it does not intersect at right angles to the line AB

When 2 lines intersect at right angles it is an altitude

so to find the line CE you want to find the co-ordinate of intersection by finding the middle point of the line AB (look in the HSN notes for the formula if you dont know it). Now you can work out the gradient of the line CE as you have co-ordinates C and E. Then its simple

You know how to find the other line since you used that method above

Finding J is easy as that point is where equation CE equals equation BD

[xClairex]

so for the mid point of AB it is:
x1+x2/2,y1 + y2 /2
which gives 7+(-3)/2 , 0+ (-2)/2 = 7-3/2 , 0-2/2 = 4/2, -2/2 = (2,-1) so point E = (2,-1)

gradient of CE = -3 so
y-y1=m(x-x1)
y-8=-3(x+1)
y-8=-3x - 3
y=-3x + 5 therefore equation CE = y + 3x = 5

and i work out equation BD = y + 2.5x = 17.5 is that right or is it completely wrong?

i know that some how i've to use simulataneous equations to solve j

when i did i got x to be -25 and y to be 42.5 but i think this is way off

[xClairex]

ye i was waaaaay off but i have figured out what i did wrong
i used the wrong points silly me lol but ive done it now