tính 1 cách hợp lý

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tính 1 cách hợp lý a,200-198+196-194+192-190+…..+8-6+4-2 b, 3 ²/8.11+3 ²/11.14+…+3 ²/2017.2020 c,1.2.3….9-1.2.3…8-1.2.3…7.8 ²

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Athena 3 tháng 2021-09-10T03:11:09+00:00 2 Answers 10 views 0

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    0
    2021-09-10T03:12:11+00:00

    a)${a,200-198+196-194+192-190+…..+8-6+4-2}$

    ${=(200-198) + (196-194) + (192-190 )+ ………+ (8-6) + (4-2)}$

    ${=2+2+2+…….+2+2}$

    ${=2.50}$

    ${=100}$

    c)${1.2.3….9-1.2.3…8-1.2.3…7.8 ²}$

    ${=1.2.3…8.(9-1-8)}$

    ${=1.2.3…8.0}$

    ${=0}$

    0
    2021-09-10T03:12:31+00:00

    a,200-198+196-194+192-190+…..+8-6+4-2

    = 2+ 2+….+ 2

    = 2. 50

    = 100

    b, $\dfrac{3^{2}}{8.11}$ +$\dfrac{3^{2}}{11.14}$…..$\dfrac{3^{2}}{2017.2020}$

    = 3. ($\dfrac{3}{8.11}$ + $\dfrac{3}{11.14}$ ….$\dfrac{3}{2017.2020}$ )

    = $3$.( $\dfrac{1}{8}$ -$\dfrac{1}{11}$ +$\dfrac{1}{11}$ -$\dfrac{1}{14}$ +…+ $\dfrac{1}{2017}$ -$\dfrac{1}{2020}$ 

    = $3$. ($\dfrac{1}{8}$ – $\dfrac{1}{2020}$ )

    = $3$. $\dfrac{503}{4040}$ 

    = $\dfrac{1509}{4040}$

    c, 1.2.3…9- 1.2.3.4.5….8- 1.2.3…7.$8^{2}$ 

    = 1.2.3…8.9- 1.2.3…8- 1.2…..8.8

    = ( 1.2…..8).( 9-8-1)

    = 8! .0

    = 0

    Chúc bạn học tốt!

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