Tính A=1/100.99-1/98.98-…..-1/3.2-1/2.1 B=(1/4.9+1/9.14+1/14.19+…+1/44.49).1-3-9-7-..-49/89 C=1/1.2.3.4+1/2.3.4.5+…+1/27.28.29.30

0 bình luận về “Tính A=1/100.99-1/98.98-…..-1/3.2-1/2.1 B=(1/4.9+1/9.14+1/14.19+…+1/44.49).1-3-9-7-..-49/89 C=1/1.2.3.4+1/2.3.4.5+…+1/27.28.29.30”

1. A=1/100.99-1/98.98-…..-1/3.2-1/2.1

     =1/9900-(1/99.98+1/98.97+1/97.96+…+1/3.2+1/2.1)

     =1/9900-(1-1/2+1/2-1/3+…+1/97-1/98+1/98+1/99)

     =1/9900-(1-1/99)

     =1/9900-98/99

     =9799/9900

   B=(1/4.9+1/9.14+1/14.19+…+1/44.49).1-3-9-7-..-49/89

     =1/5.(1/4-1/9+1/9-1/19+…+1/44-1/99.1-(3+5+…+49)/89

     =1/5.(1/4-1/49).1-(3+49).[(49-3:2+1)]/2/89

     =1/5.45/196.1-52.24/2/89

     =9/196.1-624/89

     =9/196(-623/89)

     =-9/28

   C=1/1.2.3.4+1/2.3.4.5+…+1/27.28.29.30

     =451/8120

   #chuc_hoc_tot

   cho mk xin trkhn nha

    

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