CMR:B=36/1.3.5+36/3.5.7+…..+36/25.27.29<3

0 bình luận về “CMR:B=36/1.3.5+36/3.5.7+…..+36/25.27.29<3”

1. A=36/1.3.5+36/3.5.7+36/5.7.9+…+36/25.27.29

   ⇒A=9.(4/1.3.5+4/3.5.7+4/5.7.9+…+4/25.27.29)

   ⇒A=9.(1/1.3−1/3.5+1/3.5−1/5.7+1/5.7−1/7.9+…+1/25.27−1/27.29)

   ⇒A=9.(1/1.3−1/27.29)

   ⇒A=9.(1/3−1/783)

   ⇒A=9.1/3−9.1/783

   ⇒A=3−1/87

   Vì 3−1/87<3.

   ⇒A<3

    

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2. Take it EASY !!~

   Đáp án:

   A=36/1.3.5+36/3.5.7+36/5.7.9+…+36/25.27.29

   A=36/1.3.5+36/3.5.7+36/5.7.9+…+36/25.27.29

   ⇒A=9.(4/1.3.5+4/3.5.7+4/5.7.9+…+4/25.27.29)

   ⇒A=9.(4/1.3.5+4/3.5.7+4/5.7.9+…+4/25.27.29)

   ⇒A=9.(1/1.3−1/3.5+1/3.5−1/5.7+1/5.7−1/7.9+…+1/25.27−1/27.29)

   ⇒A=9.(1/1.3−1/3.5+1/3.5−1/5.7+1/5.7−1/7.9+…+1/25.27−1/27.29)

   ⇒A=9.(1/1.3−1/27.29)

   ⇒A=9.(1/3−1/783)

   ⇒A=9.1/3−9.1/783

   ⇒A=3−1/87

   Vì 3−1/87<3.

   ⇒A<3(đpcm).

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