How to proof 4b? Thanks

4. Follow the proof of the Additivety Property in Theorem 2A.2 to show that if ce R, [ an = S, and _ b. = T, then: a. E (an-bn) = S-T = _ an - _ b., and *=0 m=0 b. Ec. an = c . S= c . _ an. Note: in part (b), there is no The "=0 Let { Un} "_ be the the partial sums of the series _ c . an. n=0