Posted by **lyne** on Monday, February 2, 2009 at 9:50pm.

function rule for tis

points- 1 2 3 4

lines- 0 1 3 6

its similar to an earlir one i posted but i still dont quite understand

thanks

- math -
**Reiny**, Monday, February 2, 2009 at 10:05pm
it deals with the number of points that a certain number of lines drawn have.

BTW, I think you have your headings backwards,

the first set of numbers should be lines,

the second set of numbers are the number of intersection points those lines have

e.g.

1 line has no intersections points

2 lines have one intersection points

3 lines have 3 intersection points

4 lines have 6 intersection points

etc.

can you see a pattern here?

- math -
**lyne**, Monday, February 2, 2009 at 10:08pm
yeaa i understand and can see the patterns i just dont know how to find the function the way you did...

- math -
**Reiny**, Monday, February 2, 2009 at 10:57pm
I don't know what grade level you are in, so I can't guess how sophisticated the method should be that I describe.

suppose we double your second line from

0 1 3 6 ... to

0 2 6 12 ...

notice that those are like

1x0, 2x1, 3x2, 4x3 .... or n(n-1)

but we multiplied our original numbers by 2, so let's divide our formula by 2 to get back to the originals.

so the function rule would be

number of points = n(n-1)/2 , where n is the number of lines drawn.

testing:

If I had 4 lines drawn, n=6

and no. of intersection points is (6x5)/2 = 15

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