+400 Let a_1, a_2, a_3, \dots be a sequence. If
a_n = a_{n - 1} + a_{n - 2}
for all n \ge 3, and a_{11} = 4 and a_{10} = 1, then find a_6.
+399 \(a_{11}=a_{10}+a_{9}\), so following this logic.
\(4=1+a_{9}\)
\(a_{9}=3\)
Similarly,
\(1=3+a_{8}\)
\(a_{8}=-2\)
\(3=-2+a_{7}\)
\(a_{7}=5\)
\(-2=5+a_{6}\)
\(a_{6}=-7\).
a6 is -7.
