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2. Si [tex]a_1=2[/tex] y [tex]a_2=3[/tex], y tenemos la relación general:
[tex]\[a_{n+1}=3a_n-2a_{n-1}\][/tex]

Hallar el valor de [tex]a_4 + a_6[/tex].

(Villareal 2011-I)

Sagot :

Para resolver el problema, vamos a utilizar la relación dada [tex]\( a_{n+1} = 3 a_n - 2 a_{n-1} \)[/tex] y los valores iniciales [tex]\( a_1 = 2 \)[/tex] y [tex]\( a_2 = 3 \)[/tex]. Queremos encontrar el valor de [tex]\( a_4 + a_6 \)[/tex].

Primero, calculemos [tex]\( a_3 \)[/tex]:

[tex]\[ a_3 = 3a_2 - 2a_1 \][/tex]

Sustituyendo [tex]\( a_2 = 3 \)[/tex] y [tex]\( a_1 = 2 \)[/tex]:

[tex]\[ a_3 = 3(3) - 2(2) \][/tex]
[tex]\[ a_3 = 9 - 4 \][/tex]
[tex]\[ a_3 = 5 \][/tex]

Ahora calculemos [tex]\( a_4 \)[/tex]:

[tex]\[ a_4 = 3a_3 - 2a_2 \][/tex]

Sustituyendo [tex]\( a_3 = 5 \)[/tex] y [tex]\( a_2 = 3 \)[/tex]:

[tex]\[ a_4 = 3(5) - 2(3) \][/tex]
[tex]\[ a_4 = 15 - 6 \][/tex]
[tex]\[ a_4 = 9 \][/tex]

A continuación, calculamos [tex]\( a_5 \)[/tex]:

[tex]\[ a_5 = 3a_4 - 2a_3 \][/tex]

Sustituyendo [tex]\( a_4 = 9 \)[/tex] y [tex]\( a_3 = 5 \)[/tex]:

[tex]\[ a_5 = 3(9) - 2(5) \][/tex]
[tex]\[ a_5 = 27 - 10 \][/tex]
[tex]\[ a_5 = 17 \][/tex]

Finalmente, calculemos [tex]\( a_6 \)[/tex]:

[tex]\[ a_6 = 3a_5 - 2a_4 \][/tex]

Sustituyendo [tex]\( a_5 = 17 \)[/tex] y [tex]\( a_4 = 9 \)[/tex]:

[tex]\[ a_6 = 3(17) - 2(9) \][/tex]
[tex]\[ a_6 = 51 - 18 \][/tex]
[tex]\[ a_6 = 33 \][/tex]

Ahora sumamos [tex]\( a_4 \)[/tex] y [tex]\( a_6 \)[/tex]:

[tex]\[ a_4 + a_6 = 9 + 33 \][/tex]
[tex]\[ a_4 + a_6 = 42 \][/tex]

Por lo tanto, el valor de [tex]\( a_4 + a_6 \)[/tex] es [tex]\(\boxed{42}\)[/tex].