Toán tinh tong: C = 1/15*18+1/18*21+…..+1/87*90 08/09/2021 By Autumn tinh tong: C = 1/15*18+1/18*21+…..+1/87*90
Đáp án: `C=1/54` Giải thích các bước giải: `C = 1/(15*18)+1/(18*21)+…..+1/(87*90)` `C = 1/3.(3/(15*18)+3/(18*21)+…..+3/(87*90))` `C = 1/3.(1/15-1/18+1/18-1/21+…..+1/87-1/90)` `C = 1/3.(1/15-1/90)` `C = 1/3. 1/18` `C=1/54` Trả lời
C= $\frac{1}{15.18}$ + $\frac{1}{18.21}$ +…+ $\frac{1}{87.90}$ = $\frac{1}{3}$ . ($\frac{3}{15.18}$ + $\frac{3}{18.21}$ +…+ $\frac{3}{87.90}$) = $\frac{1}{3}$ . ($\frac{1}{15}$ – $\frac{1}{18}$ + $\frac{1}{18}$ – $\frac{1}{21}$ +…+ $\frac{1}{87}$ – $\frac{1}{90}$) = $\frac{1}{3}$ . ($\frac{1}{15}$ – $\frac{1}{90}$) = $\frac{1}{3}$ . ($\frac{6}{90}$ – $\frac{1}{90}$) = $\frac{1}{3}$ . $\frac{5}{90}$ = $\frac{1}{54}$ Trả lời
Đáp án: `C=1/54`
Giải thích các bước giải:
`C = 1/(15*18)+1/(18*21)+…..+1/(87*90)`
`C = 1/3.(3/(15*18)+3/(18*21)+…..+3/(87*90))`
`C = 1/3.(1/15-1/18+1/18-1/21+…..+1/87-1/90)`
`C = 1/3.(1/15-1/90)`
`C = 1/3. 1/18`
`C=1/54`
C= $\frac{1}{15.18}$ + $\frac{1}{18.21}$ +…+ $\frac{1}{87.90}$
= $\frac{1}{3}$ . ($\frac{3}{15.18}$ + $\frac{3}{18.21}$ +…+ $\frac{3}{87.90}$)
= $\frac{1}{3}$ . ($\frac{1}{15}$ – $\frac{1}{18}$ + $\frac{1}{18}$ – $\frac{1}{21}$ +…+ $\frac{1}{87}$ – $\frac{1}{90}$)
= $\frac{1}{3}$ . ($\frac{1}{15}$ – $\frac{1}{90}$)
= $\frac{1}{3}$ . ($\frac{6}{90}$ – $\frac{1}{90}$)
= $\frac{1}{3}$ . $\frac{5}{90}$
= $\frac{1}{54}$