A = 1 + 3 + 3² + ..... + 3²⁰

<=> 3A = 3 + 3² + 3³ + ..... + 3²⁰ + 3²¹

<=> 3A - A = ( 3 + 3² + 3³ + .... + 3²⁰ + 3²¹ ) - ( 1 + 3 + 3² +...... + 3²⁰ )

<=> 2A = 3²¹ - 1

<=> A = ( 3²¹ - 1 ) : 2 

B = 3²¹ : 2

=> A - B = [ ( 3²¹ - 1 ) : 2 ] - [ 3²¹ : 2 ]

=> A - B = - 1

if you want to see the highest waterfall in the world, you have to go to Venezuela. there, you can find the angelfalls - a spectacular sight. we went there last year and we were very impressed. we walked in the countryside for about an hour when suddenly we heard the sound of water. as we approached the waterfall, we couldn't believe how loud the water was. it was the first time we have ever seen a waterfall and if we had known how amazing it was, we would have taken a video camera with us. we hope we will return one day to see this wonder of nature again

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