Question

[chemgio]

tính giá trị của biểu thức sau A=1/30+1/42+1/56+1/72+1/90+1/110+1/132

HELP ME!!!

Answer 1

[Tóc Em Rối Rồi Kìa]

\(A=\dfrac{1}{30}+\dfrac{1}{42}+\dfrac{1}{56}+\dfrac{1}{72}+\dfrac{1}{90}+\dfrac{1}{110}+\dfrac{1}{132}\\ =\dfrac{1}{5\cdot6}+\dfrac{1}{6\cdot7}+\dfrac{1}{7\cdot8}+\dfrac{1}{8\cdot9}+\dfrac{1}{9\cdot10}+\dfrac{1}{10\cdot11}+\dfrac{1}{11\cdot12}\\ =\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}+...+\dfrac{1}{11}-\dfrac{1}{12}\\ =\dfrac{1}{5}-\dfrac{1}{12}\\ =\dfrac{12}{60}-\dfrac{5}{60}=\dfrac{7}{60}\)

Answer 2

[chemgio]

thank bạn nhìu nha