1/10 + 1/15 + 1/21 + … + 1/120 . Tính giùm mình nha 09/11/2021 Bởi Josie 1/10 + 1/15 + 1/21 + … + 1/120 . Tính giùm mình nha
Đáp án: Giải thích các bước giải: Đặt $A=$ $\frac{1}{10}$+ $\frac{1}{15}$+ $\frac{1}{21}$+…+ $\frac{1}{120}$ ⇒$\frac{1}{2}$$A=$$\frac{1}{20}$+ $\frac{1}{30}$+ $\frac{1}{42}$+…+ $\frac{1}{240}$ ⇔$\frac{1}{2}$$A=$$\frac{1}{4.5}$+ $\frac{1}{5.6}$+ $\frac{1}{6.7}$+…+ $\frac{1}{15.16}$ ⇔$\frac{1}{2}$$A=$$\frac{1}{4}$- $\frac{1}{5}$+ $\frac{1}{5}$- $\frac{1}{6}$+ $\frac{1}{6}$- $\frac{1}{7}$+…+ $\frac{1}{15}$- $\frac{1}{16}$ ⇔$\frac{1}{2}$$A=$ $\frac{1}{4}$-$\frac{1}{16}$=$\frac{12}{64}$= $\frac{3}{16}$ ⇒$A= $$\frac{3}{8}$ Bình luận
Đáp án: A =1/10+1/15+1/21+…..+1/120 1/2A = 1/20+1/30+1/42+…1/240 1/2A= 1/4×5+1/5×6+1/6×7+…1/15×16 1/2A = (1/4-1/5)+(1/5-1/6)+(1/6-1/7)+…+ (1/15-1/16) 1/2A = 1/4 – 1/6 1/2A = 3/16 A = 3/16 x 2 A = 3/8 Chúc bạn học tốt! Cho mình vote + cám ơn + ctlhn!^_^ Bình luận
Đáp án:
Giải thích các bước giải:
Đặt $A=$ $\frac{1}{10}$+ $\frac{1}{15}$+ $\frac{1}{21}$+…+ $\frac{1}{120}$
⇒$\frac{1}{2}$$A=$$\frac{1}{20}$+ $\frac{1}{30}$+ $\frac{1}{42}$+…+ $\frac{1}{240}$
⇔$\frac{1}{2}$$A=$$\frac{1}{4.5}$+ $\frac{1}{5.6}$+ $\frac{1}{6.7}$+…+ $\frac{1}{15.16}$
⇔$\frac{1}{2}$$A=$$\frac{1}{4}$- $\frac{1}{5}$+ $\frac{1}{5}$- $\frac{1}{6}$+ $\frac{1}{6}$- $\frac{1}{7}$+…+ $\frac{1}{15}$- $\frac{1}{16}$
⇔$\frac{1}{2}$$A=$ $\frac{1}{4}$-$\frac{1}{16}$=$\frac{12}{64}$= $\frac{3}{16}$
⇒$A= $$\frac{3}{8}$
Đáp án:
A =1/10+1/15+1/21+…..+1/120
1/2A = 1/20+1/30+1/42+…1/240
1/2A= 1/4×5+1/5×6+1/6×7+…1/15×16
1/2A = (1/4-1/5)+(1/5-1/6)+(1/6-1/7)+…+ (1/15-1/16)
1/2A = 1/4 – 1/6
1/2A = 3/16
A = 3/16 x 2
A = 3/8
Chúc bạn học tốt!
Cho mình vote + cám ơn + ctlhn!^_^