Lời giải:
\(A=3\left(\frac{5-2}{2.5}+\frac{8-5}{5.8}+\frac{11-8}{8.11}+\frac{14-11}{11.14}+\frac{17-14}{14.17}\right)\)
\(=3\left(\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+\frac{1}{14}-\frac{1}{17}\right)\\ =3\left(\frac{1}{2}-\frac{1}{17}\right)=\frac{45}{34}\)
`A=(3^2)/(2.5) + (3^2)/(5.8) + (3^2)/(8.11) + (3^2)/(11.14) + (3^2)/(14.17)`
`=3(3/(2.5) + 3/(5.8) + 3/(8.11) + 3/(11.14) + 3/(14.17))`
`=3.(1/2 - 1/5 + 1/5 - 1/8 + 1/8 -1/11 + 1/11 - 1/14 + 1/14 -1/17)`
`=3.(1/2 - 1/17)`
`=3. 15/34`
`=45/34`
Vậy `A=45/34`
