-BE = -a -3b
--ME = 1/2 (-a-3b)
--AM = -3b -2a + 1/2 (a + 3b)
AM = -3b -2a + 1/2a + 3/2b
AM = -3/2b -3/2a
AM = -3/2 (b + a)
--AD = -2a -2b
AD = -2(a + b) Therefore, A, M, D are on a straight line because they have the same multiply.
I Hope This Helped. Just follow the signs. If you go the opposite way to the direction of the arrow then it is negative. You need to write a sentence using the keywords 'same multiply'. And make sure to factorise for example I did -3/2b -3/2a would be -3/2 (b + a), because -3/2 is common. We know that it is a parallelogram so the sides will e equal. I got 3b because CD + DE is the same as 2b + b which adds up to 3b. If you don't understand, try maths genie or watch a video on youtube. I wish you the best of luck.