The general term of the series is
Tr=1+4r4r.
Factorizing the denominator:
1+4r4=(1+2r2)2−4r2=(2r2−2r+1)(2r2+2r+1)Thus,
Tr=(2r2−2r+1)(2r2+2r+1)rMultiplying and dividing by
4:
Tr=41[(2r2−2r+1)(2r2+2r+1)4r]Tr=41[2r2−2r+11−2r2+2r+11]The sum of the first
10 terms is:
S10=∑r=110Tr=41∑r=110(2r2−2r+11−2(r+1)2−2(r+1)+11)This is a telescoping series, so all intermediate terms cancel out:
S10=41[(11−51)+(51−131)+…+(2(10)2−2(10)+11−2(10)2+2(10)+11)]S10=41[1−2211]=41(221220)=22155Given
S10=nm and
gcd(m,n)=1.
Here,
m=55 and
n=221. Since
55=5×11 and
221=13×17,
gcd(55,221)=1.
Therefore,
m+n=55+221=276.
Answer:
276