# Is there a way. Arithmetic Progressions. Again

• March 6th 2011, 10:47 AM
jubmamie
Is there a way. Arithmetic Progressions. Again
I need help again. I'm stuck on something.

If, in an Arithmetic Progression, U5 (5 term) =-.05 and the sum of the first 7 terms = 21, how can we find the first term?
• March 6th 2011, 11:06 AM
e^(i*pi)
Nth term: $U_n = a+(n-1)d$

Sum of n terms: $S_n = \dfrac{n}{2}(2a+(n-1)d)$

Plug in what you know and solve for a