Arithmetic Sequence

• Nov 15th 2012, 09:43 PM
Vince604
Arithmetic Sequence
In an arithmetic sequence, the 11th term is 53 and the sum ofof the 5th and 7th terms is 56. Find the first 3 terms of the sequence.

I'm trying to use the formula: tn= t1+(n-1)d but cant figure out where to get the numbers. Please step by step on how to get answer would be really helpful. Thanks
• Nov 15th 2012, 09:51 PM
MarkFL
Re: Arithmetic Sequence
Using the given information, we obtain two equations in two unknowns:

\$\displaystyle t_1+10d=53\$

\$\displaystyle (t_1+4d)+(t_1+6d)=56\,\therefore\,2t_1+10d=56\$

If we subtract the first equation from the second, we will eliminate \$\displaystyle d\$ and we can solve for \$\displaystyle t_1\$. Then we can use this value to find \$\displaystyle d\$ from either of the original equations.
• Nov 16th 2012, 01:47 AM
Vince604
Re: Arithmetic Sequence
is t1 = 3?
• Nov 16th 2012, 01:51 AM
MarkFL
Re: Arithmetic Sequence
Yes, so what is d?
• Nov 16th 2012, 01:54 AM
Vince604
Re: Arithmetic Sequence
oh sweet thanks so much! d=5 i got it now. everything fell into place :)
• Nov 16th 2012, 02:06 AM
MarkFL
Re: Arithmetic Sequence
Yes, good work! :)