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If a1= 7 and an= -4an-1 + 5 then find the value of a4.

1 Answer

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Given that


\begin{gathered} a_1=7 \\ a_{_{}n}=-4a_{n-1_{}}+5 \end{gathered}

Hence,


\begin{gathered} a_2=-4a_1+5 \\ =-4(7)+5 \\ -28+5=-23 \end{gathered}

Similarly,


\begin{gathered} a_3=-4a_2+5 \\ a_3=-4(-23)+5 \\ =92+5=97 \end{gathered}

Therefore,


\begin{gathered} a_4=-4a_3+5 \\ a_4=-4(97)+5 \\ =-388+5 \\ =-383 \\ \\ a_4=-383 \end{gathered}

User Jean Regisser
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