C2: sequences and series

Hi,

I'm using a the formula to find the sum of a series but I can't get the right answer. Would anyone be able to tell me where I'm going wrong?

$\displaystyle\sum_{n=10}^{509} 4n-37$

So I worked out the first, second and third terms, getting 3, 7 and 11 respectively. So I knew a=3, d=4. I then used (n/2)[2a + (n-1)d] so
254.5(6+2032) giving 518,671 but this is the wrong answer. Have I applied the wrong formula? I thought it was the one to use as it is an arithmetic series and I have all the numbers...

Any help would be appreciated!
Marc

Hi,

I'm using a the formula to find the sum of a series but I can't get the right answer. Would anyone be able to tell me where I'm going wrong?

$\displaystyle\sum_{n=10}^{509} 4n-37$

So I worked out the first, second and third terms, getting 3, 7 and 11 respectively. So I knew a=3, d=4. I then used (n/2)[2a + (n-1)d] so
254.5(6+2032) giving 518,671 but this is the wrong answer. Have I applied the wrong formula? I thought it was the one to use as it is an arithmetic series and I have all the numbers...

Any help would be appreciated!
Marc