Tìm giá trị biểu thức:
a) P=\(\dfrac{5}{6}\)+\(\dfrac{5}{12}\)+\(\dfrac{5}{20}\)+\(\dfrac{5}{30}\)+\(\dfrac{5}{42}\)+\(\dfrac{5}{56}\)+\(\dfrac{5}{72}\)+\(\dfrac{5}{90}\)
b) A=\(\dfrac{3}{1.5}\)+\(\dfrac{3}{5.9}\)+\(\dfrac{3}{9.13}\)+...+\(\dfrac{3}{61.65}\). Chứng minh A<13.
Mik đag cần gấppp!!! Thanks!