2/(1*4)+2/(4*7)+2/(7*10)+2/(10*13)+...+2/(3n-2)(3n+1)快点,我明天就要交了

2/(1*4)+2/(4*7)+2/(7*10)+2/(10*13)+...+2/(3n-2)(3n+1)快点,我明天就要交了
2/(1*4)+2/(4*7)+2/(7*10)+2/(10*13)+...+2/(3n-2)(3n+1)
快点,我明天就要交了

2/(1*4)+2/(4*7)+2/(7*10)+2/(10*13)+...+2/(3n-2)(3n+1)快点,我明天就要交了
拆项法 原式=2/3(1-1/4+1/4-1/7+1/7.-1/(3n-2)+1/(3n12)-1/(3n+1))=2/3(1-1/(3n+1))=2n/(3n+1)