Đáp án:
Giải thích các bước giải:
$S=$$\dfrac{3}{1.4}$+ $\dfrac{3}{4.7}$+$\dfrac{3}{7.10}$+...+ $\dfrac{3}{40.43}$+ $\dfrac{3}{43.46}$
$=$$\dfrac{1}{1}$-$\dfrac{1}{4}$+$\dfrac{1}{4}$-$\dfrac{1}{7}$+ $\dfrac{1}{7}$- $\dfrac{1}{10}$+...+ $\dfrac{1}{40}$- $\dfrac{1}{43}$+$\dfrac{1}{43}$- $\dfrac{1}{46}$
$=$$1-$$\dfrac{1}{46}$$<1$
