Đáp án:
`⇒y=\frac{2000}{21}`
Giải thích các bước giải:
`(\frac{3}{1.5}+\frac{3}{5.9}+...+\frac{3}{39.43})y=\frac{3000}{43}`
`(\frac{4}{1.5}+\frac{4}{5.9}+...+\frac{4}{39.43})\frac{3}{4}y=\frac{3000}{43}`
Áp dụng `\frac{4}{n(n+4)}=\frac{1}{n}-\frac{1}{n+4}`
`⇒(1-\frac{1}{5}+\frac{1}{5}-\frac{1}{9}+...+\frac{1}{39}-\frac{1}{43}).\frac{3}{4}y=\frac{3000}{43}`
`⇒(1-\frac{1}{43})y=\frac{3000}{43}:\frac{3}{4}`
`⇒\frac{42}{43}y=\frac{4000}{43}`
`⇒y=\frac{4000}{43}:\frac{42}{43}`
`⇒y=\frac{2000}{21}`
