Question

tính A = \(\dfrac{3}{1^2.2^2}+\dfrac{5}{2^2.3^2}\)

Answer 1

\(A=\dfrac{3}{1^2.2^2}+\dfrac{5}{2^2.3^2}=\dfrac{2^2-1^2}{1^2.2^2}+\dfrac{3^2-2^2}{2^2.3^2}=1-\dfrac{1}{2^2}+\dfrac{1}{2^2}-\dfrac{1}{3^2}=1-\dfrac{1}{9}=\dfrac{8}{9}\)

Answer 2

\(A=\dfrac{3}{1^2.2^2}+\dfrac{5}{2^2.3^2}=\dfrac{3}{1.4}+\dfrac{5}{4.9}=\dfrac{3}{4}+\dfrac{5}{36}=\dfrac{27}{36}+\dfrac{5}{36}=\dfrac{32}{36}=\dfrac{8}{9}\)