C1:cho A=196/197+197/198 B=197+197/197+198 so nao lon hon C2:1/4+1/5+1/6+...+1/19 chung to B<1 C3:B=1/2^2+1/3^2+1/4^2+1/5^2+1/6^2+1/7^2+1/8^2 chung to B<1 giup mik voi minh cam on truoc

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