Đáp án:
Ta có :
A = (1 - $\frac{1}{3}$ ) +( 1-$\frac{1}{15}$ ) - (1- $\frac{1}{35}$ ) + ( 1 - $\frac{1}{63}$ ) + ( 1- $\frac{1}{99}$ ) + (1- $\frac{1}{143}$ ) + 1 - ($\frac{1}{195}$ )
⇒ A = 7 - ($\frac{1}{3}$ + $\frac{1}{15}$ + $\frac{1}{35}$ + $\frac{1}{63}$ + $\frac{1}{99}$ + $\frac{1}{143}$ + $\frac{1}{195}$ )
⇒ A = 7 - $\frac{1}{2}$ . ( $\frac{1}{1.3}$ + $\frac{1}{3.5}$ + $\frac{1}{5.7}$ + $\frac{1}{7.9}$ + $\frac{1}{9.11}$ +$\frac{1}{11.13}$ +$\frac{1}{13.15}$ ) = 7 - $\frac{1}{2}$ . ( 1 - $\frac{1}{15}$ ) = 7 - 1/2.14/15 = 7 - 7/15 =98/15 > 75/15 = 5
B = 5 - 1/2^2 + 1/3^3 + 1/4^4 + 1/5^5 + 1/6^6 + 1/7^7 < 5
⇒ A>5>B ⇒ A >B
