=1/45

= \(1 + \frac{1}{3} + 1 + \frac{1}{9} + 1 + \frac{1}{27} + . . . + 1 + \frac{1}{3^{98}}\)\(\frac{1}{3^{98}}\)

\(= 1.98 + \left(\right. \frac{1}{3} + \frac{1}{3^{2}} + \frac{1}{3^{3}} + . . . + \frac{1}{3^{98}} \left.\right)\)

Đặt A=\(\frac{1}{3} + \frac{1}{3^{2}} + \frac{1}{3^{3}} + . . . + \frac{1}{3^{98}}\)

\(\Rightarrow 3 A = 1 + \frac{1}{3} + \frac{1}{3^{2}} + . . . + \frac{1}{3^{97}}\)

\(\Rightarrow 3 A - A = 2 A = 1 - \frac{1}{3^{98}} \Rightarrow A = \frac{1 - \frac{1}{2^{98}}}{2} < 1\)

\(\Rightarrow B = 98 + A < 98 + 1 < 99 < 100\)

\(\Rightarrow B < 100\)

2 x 2 + 2 x 2 + 2 - 2 x 2

= 4+ 4 +2 - 4

=8 + 2 -4

= 10 -4

= 6

2 x 2 =2 + 2 =4

a ) R\(−3;1]=(-∞;-3]∪(1;+∞)

b)  [-2; \, 0](−∞;1)\[−2;0]= [-2; \, 0]∞;-2)∪(0;1)