Question

ajutatime 5+5la a 2 +5la a 3+5la a 4............s la 101

Answer 1

S=5+$5^{2} + 5^{3} + 5^{4} ....................+ 5^{101}$            |-
2S=$5^{2} + 5^{3} + 5^{4} + 5^{5} +.....................+ 5^{102}$|-
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S=$5^{102} -5$