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# C1 parallelogram graph question watch

1. hi, I am a bit stuck on part b and c of this question. To solve this, apparently line Ad is perpendicular to l1 but how can that be as the angle in between isn't a right angle. I know that l1 and l2 are parallel and the other two lines are as well. Thanks.
2. I need someone to explain why AD would be perpendicular to l1... Thanks in advance.
3. It's a parrallelogram so It can't be a right angle
4. (Original post by lytran)
It's a parrallelogram so It can't be a right angle
...I, say what? A rectangle is a parallelogram... what are the angles in a rectangle?
5. (Original post by Zacken)
...I, say what? A rectangle is a parallelogram... what are the angles in a rectangle?
But in that question , it didnt say a rectangle so i just assume that it's just this one
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6. (Original post by coconut64)
hi, I am a bit stuck on part b and c of this question. To solve this, apparently line Ad is perpendicular to l1 but how can that be as the angle in between isn't a right angle. I know that l1 and l2 are parallel and the other two lines are as well. Thanks.
In answer to your question, AD is not perpendicular to , either you are reading wrong or the markscheme is wrong. What I suspect is happening is that you are reading wrong and that the mark scheme is finding a line that passes through A and is perpendicular to but this does not imply that the line also passes through D.
7. (Original post by Zacken)
In answer to your question, AD is not perpendicular to , either you are reading wrong or the markscheme is wrong. What I suspect is happening is that you are reading wrong and that the mark scheme is finding a line that passes through A and is perpendicular to but this does not imply that the line also passes through D.
Yeah , sorry my mistake. I got confused that's why. So this is what I think is happening: find the perpendicular line to L1 going through A. Then find the point of intersection with L2. Then work out the distance between A and the point of intersection? Right?
8. (Original post by coconut64)
Yeah , sorry my mistake. I got confused that's why. So this is what I think is happening: find the perpendicular line to L1 going through A. Then find the point of intersection with L2. Then work out the distance between A and the point of intersection? Right?
Yes.
9. (Original post by Zacken)
Yes.
Great. So this distance is the same as the length of AD/ bc ? Because for part c, they used length of AB and the distance found in the previous part of the question.
10. (Original post by coconut64)
So this distance is the same as the length of AD/ bc ? Because for part c, they used length of AB and the distance found in the previous part of the question.
Well... no - look up the definition of an area of a parallelogram, it's the side * perpendicular height. Not side * side. You can find the length AB and you've just found the perpendicular height, not AD.

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