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DAU COROANA

Aflati suma S=1+[tex]\frac{1}{5}[/tex]+[tex]\frac{1}{5^{2} }[/tex]+...+[tex]\frac{1}{5^{11} }[/tex]


Răspuns :

[tex]\it \dfrac{..}{..}\ \ b_1+b_2+b_3+\ ...\ +b_n= b_1\cdot\dfrac{q^n-1}{q-1}\\ \\ \\ 1+\dfrac{1}{5}+\dfrac{1}{5^2}+\dfrac{1}{5^3}+\ ...\ +\dfrac{1}{5^{11}}=\ \dfrac{\ \dfrac{1}{5^{12}}-1}{\dfrac{1}{5}-1}=\dfrac{5^{12}-1}{5^{12}}\cdot\dfrac{5}{4}=\dfrac{5^{12}-1}{4\cdot5^{11}}[/tex]

Răspuns:

aplici formula invatata pe 1+x+x²+...+x^n

Explicație pas cu pas:

(1-(1/5)^12)/(1-1/5) =((5/4)*(5^12-1))/5^12)=(5^13-5)/4*5^12=(5^12-1)/4*5^11=

5/4-1/(4*5^11)