Coordinate Geometry
posted by Jitesh .
Please help!!!!!
The points A,B,C,D have coordinates (3,3), (8,0), (1,1), (6,4) respectively.
a) Find the gradients of the lines AB and CD
b) Show that ABCD is a parallelogram
c) Find the coordinates of the point of intersection of the diagnols AC and BD.
Please help me by showing all methods of working out answer.

I assume that by gradient you mean slope, m
m AB = (03)/(83) = 3/5
m CD = (41)/(6+1) = 35
so AB and CD are parallel (same slope)
if DA and CB are also parallel, it is a parallelogram
m DA = (43)/(63) = 1/9
m CB = (01)/(8+1) = 1/9
sure enough, parallelogram
where is the middle?
halfway between A and C (or D and B)
do A and C
average x = (1 + 3)/2 = 1
average y = (1+3)/2 = 2
so (1,2)