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.
an=an−1+an−2
an−2=an−an−1
a9=4−1=3
a8=1−3=−2
a7=3−(−2)=5
a6=−2−5=−7.
+2729 
+410 
