Maths genius needed :(

Hey guys,
So I'm having a bit of trouble with an AS OCR C1 coordinate geometry question, I just can't understand what its asking me to do. I don't want the answer, I just want to know a breakdown of how to approach it:

"Find the equation of the straight line L through P(7,5) perpendicular to the straight line AB whose equation is 3x + 4y - 16 = 0."

I am terrible at visualising things like this, but my thought is that line L is parallel to line AB?

Thank you so much for any help!!!! :tongue:

Reply 1

Muttley79

20

Original post by Georgiam247

Hey guys,
So I'm having a bit of trouble with an AS OCR C1 coordinate geometry question, I just can't understand what its asking me to do. I don't want the answer, I just want to know a breakdown of how to approach it:

"Find the equation of the straight line L through P(7,5) perpendicular to the straight line AB whose equation is 3x + 4y - 16 = 0."

I am terrible at visualising things like this, but my thought is that line L is parallel to line AB?

Thank you so much for any help!!!! :tongue:

You are looking for a line perpendicular to 3x + 4y - 16 = 0 so find the gradient of that line first.

Reply 2

Indeterminate

3

Original post by Georgiam247

Hey guys,
So I'm having a bit of trouble with an AS OCR C1 coordinate geometry question, I just can't understand what its asking me to do. I don't want the answer, I just want to know a breakdown of how to approach it:

"Find the equation of the straight line L through P(7,5) perpendicular to the straight line AB whose equation is 3x + 4y - 16 = 0."

I am terrible at visualising things like this, but my thought is that line L is parallel to line AB?

Thank you so much for any help!!!! :tongue:

Perpendicular lines have the property that the product of their respective gradients is -1

Then use P in the usual formula, namely

y-y_1 = m(x-x_1)

Reply 3

SerpentPlumes

3

Here's a visual of what perpendicular means. Have you had any experience working out the gradient of a perpendicular line?

Reply 4

Georgiam247

OP

2

Original post by SerpentPlumes

Here's a visual of what perpendicular means. Have you had any experience working out the gradient of a perpendicular line?

Yes I have, I find it quite easy usually. It was just the wording of the question, the addition of 'P' confused me.

I got the correct answer which was '4x-3y-13=0' but there is a part b) and c) to this question which I have no idea how to approach whatsoever..

b) Find the point of intersection of the line AB with the line L in part a).

c) Hence find the perpendicular distance from P to AB

I'm completely lost :frown:

Reply 5

SerpentPlumes

3

Original post by Georgiam247

Yes I have, I find it quite easy usually. It was just the wording of the question, the addition of 'P' confused me.

I got the correct answer which was '4x-3y-13=0' but there is a part b) and c) to this question which I have no idea how to approach whatsoever..

b) Find the point of intersection of the line AB with the line L in part a).

c) Hence find the perpendicular distance from P to AB

I'm completely lost :frown:

Okay, so you have the equation of L. Now, for part b, you need to work out when the line L and the line AB have the same x and y value. Once you've got that worked out, for part c you're essentially trying to find the distance from point P to the point of intersection (because the line from the intersection point to the point P is perpendicuar to AB).

Does that make sense? Can you do all of that?

Maths genius needed :(

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