Răspuns
S=1+2¹+2²+2³+2⁴+...+2⁴⁰ adaugam 1 si dupa il luam:
S=1+1+2¹+2²+2³+2⁴+...+2⁴⁰-1
S=2+2¹+2²+2³+2⁴+...+2⁴⁰-1
Observam : 2+2¹=2+2=2*2=2² =>
S=2²+2²+2³+2⁴+.....+2⁴⁰-1
Observam : 2²+2²=2²(1+1)=2³ =>
S=2³+2³+2⁴+...+2⁴⁰-1
La fel : 2³+2³=2³(1+1)=2*2³ =2⁴
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In final obtinem :
S=2⁴⁰+2⁴⁰ - 1=2⁴⁰·(1+1) - 1=2·2⁴⁰-1 = 2⁴¹-1
Explicație pas cu pas: