1. ## Straight Lines

Hi there,

I'm having a little bit of a problem with a simple question, that I know the answer to, but don't know the working to get the answer.

The question is as follows:

A(-2, 2) and C(3, -1) are opposite vertices of kite ABCD. Find the gradient of diagonal BD.

I know the answer is 5/3 but I don't know *how* that is the answer.
If someone could possibly tell me the formula, it would put my mind at rest.

Thanks!

2. Originally Posted by Mathy
...

The question is as follows:

A(-2, 2) and C(3, -1) are opposite vertices of kite ABCD. Find the gradient of diagonal BD.
...
Hello,

you are supposed to know that in a kite the diagonals are perpendicular to each other. Therefore

1. calculate the slope (=gradient) between A and B
2. calculate the perpendicular slope. That must be the slope between BD

$\displaystyle m=\frac{2-(-1)}{-2-3}=-\frac{3}{5}$

The perpendicular slope is the negative reziprocal value of m. Thus $\displaystyle m'=\frac{5}{3}$

3. Yay!

Thank you. This was my original thought, but I thought that the it may have needed more.

I'm all happy now.