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?
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Nth term: $\displaystyle U_n = a+(n-1)d$ Sum of n terms: $\displaystyle S_n = \dfrac{n}{2}(2a+(n-1)d)$ Plug in what you know and solve for a
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