C = $\frac{1}{2}$ + $\frac{1}{6}$ + $\frac{1}{12}$ + $\frac{1}{20}$ + … + $\frac{1}{110}$
GIẢI HỘ TUI T^T
C = $\frac{1}{2}$ + $\frac{1}{6}$ + $\frac{1}{12}$ + $\frac{1}{20}$ + … + $\frac{1}{110}$ GIẢI HỘ TUI T^T
By Aaliyah
By Aaliyah
C = $\frac{1}{2}$ + $\frac{1}{6}$ + $\frac{1}{12}$ + $\frac{1}{20}$ + … + $\frac{1}{110}$
GIẢI HỘ TUI T^T
Đáp án:
Ta có :
`C = 1/2 + 1/6 + 1/12 + 1/20 + …+ 1/110`
` = 1/(1.2) + 1/(2.3) + 1/(3.4) + …. + 1/(10.11)`
` = 1 – 1/2 + 1/2 – 1/3 + 1/3 – 1/4 + … + 1/10 – 1/11`
` = 1 – 1/11`
` = 10/11`
Giải thích các bước giải:
`C = 1/2 + 1/6 + 1/12 + 1/20 +…+1/110`
`C =` $\dfrac{1}{1 × 2}$ + $\dfrac{1}{2 × 3}$ + $\dfrac{1}{3 × 4}$ +…+ $\dfrac{1}{10 × 11}$
`= 1/1 – 1/2 + 1/2 – 1/3 + 1/3 – 1/4 + 1/4 -….+1/10 – 1/10 + 1/11 – 1/11`
`= 1 – 1/11 = 10/11`
⇔ `C = 10/11`