# Math Help - Is there a way. Arithmetic Progressions. Again

1. ## 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?

2. 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