Răspuns :
S=1 + 3+ 3² + ... + 3⁴⁹ inmultim cu 3
3S=3+3²+3³+....3⁵⁰
3S+1=1+3+3²+3³+....3⁵⁰
3S+1=S+3⁵⁰
3S-S=3⁵⁰-1
2S=3⁵⁰-1
S=(3⁵⁰-1)/2
2×(3⁵⁰-1)/2=3⁵⁰-1
3S=3+3²+3³+....3⁵⁰
3S+1=1+3+3²+3³+....3⁵⁰
3S+1=S+3⁵⁰
3S-S=3⁵⁰-1
2S=3⁵⁰-1
S=(3⁵⁰-1)/2
2×(3⁵⁰-1)/2=3⁵⁰-1