\(\dfrac{3}{1.4}+\dfrac{3}{4.7}+\dfrac{3}{7.10}+...+\dfrac{3}{27.30}\)
\(=1-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{10}+...+\dfrac{1}{27}-\dfrac{1}{30}\)
\(=1-\dfrac{1}{30}\)
\(=\dfrac{29}{30}\)
Chúc bạn học tốt
A= 3/1.4+ 3/4.7+ 3/7.10+...+ 3/27.30
= 1/3 . ( 3- 3/4 + 3/4- 3/7 +3/7- 3/10+... + 3/27- 3/30)
= 1/3 . (3 - 3/30)= 1/3 . 87/30= 87/90=29/30
Lời giải:
\(A=\dfrac{3}{1.4}+\dfrac{3}{4.7}+\dfrac{3}{7.10}+...+\dfrac{3}{27.30}\)
\(A=1-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+...+\dfrac{1}{27}-\dfrac{1}{30}\)
\(A=1-\dfrac{1}{30}\)
\(A=\dfrac{29}{30}\)
