A = 1/10 + 1/15 + 1/21 + ....+ 1/120
= 2/20 + 2/30 + 2/42 +....+ 2/240
= 2/4x5 + 2/5x6 + 2/6x7 + ...+ 2/15x16
= 2 x ( 1/4x5 + 1/5x6 + 1/6x7 +...+ 1/15x16)
=2 x ( 1/4 - 1/5 + 1/5 - 1/6 +1/6 - 1/7 + .....+ 1/15 - 1/16 )
= 2 x ( 1/4 - 1/16 )
= 2 x ( 4/16 - 1/16 )
= 2 x 3/16
= 6/16
= 3/8
tk nhé
tính nhanh:
C = 1/10 + 1/15 + 1/21 +.......+ 1/120
1/1.4+1/4.7+1/7.10+.......+1/16.19
1/10=1/15+1/21+........+1/120
Tính nhanh (nếu có thể).
Tính nhanh:
C= 1/10 + 1/15 + 1/21...........+1/120
Tính nhanh: N = \(\frac{1}{10}+\frac{1}{15}+\frac{1}{21}+...+\frac{1}{120}\)
Tính nhanh
\(B=\frac{1}{10}+\frac{1}{15}+\frac{1}{21}+...+\frac{1}{120}\)
Tính nhanh: A= 3.136. 8+ 4.14. 6- 14.150
C= 1/10 + 1/15 + 1/21...........+1/120
\(y=\frac{1}{10}+\frac{1}{15}+\frac{1}{21}+.....+\frac{1}{120}\)
Tính tổng dãy số
1/10+1/15+1/21+...+1/120 = ?
1/10+1/15+1/21+......+1/120 = ?
