Question

Tính các tổng sau 

,\(a,A=2+2^3+2^5+2^7+2^9+...+2^{2009}\)

\(b,B=1+2^{^2}+2^4+2^6+2^8+2^{10}+...+2^{200}\)

\(c,C=5+5^3+5^5+5^7+5^9+...+5^{101}\)

Answer 1

mình chỉ làm câu b) thôi nhé.Còn các câu khác cậu làm tương tự

B=1+2^2+2^4+2^6+2^8+2^10+...+2^200

2^2B=2^2.(1+2^2+2^4+2^6+2^8+2^10+...+2^200)

2^2B=2^2+2^4+2^6+2^8+2^10+2^12+...+2^201

2^2B-2B=(2^2+2^4+2^6+2^8+2^10+2^11+...+2^201)-(1+2^2+2^4+2^6+2^8+2^10+...+2^200)

2B=2^201-1

B=(2^201-1):2