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Calculați valoarea sunei 
S= 1 + E(2) +E(2^2) +..............+E(2^40) Stiind ca E(x)= x Urgentt ofer 20 p si coroana


Răspuns :

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: