## tính 1 cách hợp lý

Question

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

## Answers ( )

1. 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)${1.2.3….9-1.2.3…8-1.2.3…7.8 ²}$

${=1.2.3…8.(9-1-8)}$

${=1.2.3…8.0}$

${=0}$

2. 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!