Question

Please help me with the problems

Answer 1

Sure. The formula for an infinite geometric series with first term a and common ratio r says it converges when |r|<1; in that case the sum is

`S = (a)/(1-r)`

Q3. r=-4/5 (converges), a=5, S=5/(1- -4/5) = 5/(9/5) = 25/9

Answer: a

Q4. r=1/6 (converges), a=420, S=420/(1-1/6) = 420/(5/6) = 6(84) = 504

Answer: a

Q5. r=1.2, diverges