1.3.5+3.5.7+5.7.9+...+97.99.101

=(101-2).(101-1).101.(101+1):4

=25497450

A = 1/4.( 4/1.3.5 + 4/3.5.7+ ....+ 4/95.97.99)

    = 1/4 .( 1/ 1.3 - 1/3.5 + 1/3.5 - 1/5.7 + .......+ 1/95.97 - 1/97.99)

   = 1/4( 1/1.3 - 1/97.99)

    = 1/4 . 9499/29397

\(G=1.3.5+3.5.7+5.7.9+...+95.97.99\)

\(G=1+99.\left(3+5+7+...+97\right)\)\

\(G=100.\left[\left(3+97\right)+\left(5+95\right)+...+\left(49+51\right)\right]\)

\(G=100.\left(100.24\right)\)

\(G=100.2400=240000\)

240000

\(A=\frac{1}{1.3.5}+\frac{1}{3.5.7}+\frac{1}{5.7.9}+...+\frac{1}{95.97.99}\)

\(A=4.\left(\frac{1}{1.3}-\frac{1}{3.5}+\frac{1}{3.5}-\frac{1}{5.7}+\frac{1}{5.7}-\frac{1}{7.9}+...+\frac{1}{95.97}-\frac{1}{97.99}\right)\)

\(A=4.\left(\frac{1}{1.3}-\frac{1}{97.99}\right)\)

\(A=4.\frac{3200}{9603}=\frac{12800}{9603}\)

\(A=\frac{1}{1.3.5}+\frac{1}{3.5.7}+\frac{1}{5.7.9}+...+\frac{1}{95.97.99}\)

\(A=\frac{1}{4}.\left(\frac{1}{1.3.5}+\frac{1}{3.5.7}+\frac{1}{5.7.9}+...+\frac{1}{95.97.99}\right)\)

\(A=\frac{1}{4}.\left(\frac{1}{1.3}-\frac{1}{3.5}+\frac{1}{3.5}-\frac{1}{5.7}+\frac{1}{5.7}-\frac{1}{7.9}+...+\frac{1}{95.97}-\frac{1}{97.99}\right)\)

\(A=\frac{1}{4}.\left(\frac{1}{1.3}-\frac{1}{97.99}\right)\)

\(A=\frac{1}{4}.\frac{3200}{9603}\)

\(A=\frac{800}{9603}\)

Bài trc mik làm lộn :)))
~ Hok tốt ~
 

8A = 1.3.5.8 + 3.5.7.8 + 5.7.9.8 + … + 95.97.99. = 1.3.5(7 + 1) + 3.5.7(9 - 1) + 5.7.9(11 - 3) +… +95.97.99(101 - 93) = 1.3.5.7 + 15 + 3.5.7.9 - 1.3.5.7 + 5.7.9.11 - 3.5.7.9 + …+ 95.97.99.101 - 93.95.97.99 = 15 + 95.97.99.101 8A={15+95.97.99.101}/{8} = 11 517 61313 ko bt có đúng ko,chúc bn học tốt