Question

Find the first six terms of the sequence. a1 = 4, an = 2 • an-1

Answer 1

Hello : 
1) a1 = 4,    an = 2 • an-1
this is a geometric sequence the first terme is ; a1 = 4 and common ratio : r =2
the general term is : an = a1 × r^(n-1)
an = 4 ×2^(n-1).....(*) 
the first six terms is : a1 , a2 , a3 , a4 , a5 , a6
put ; n = 1, 2 , 3 , 4 , 5  in : (*).....calculate.
2) same idea ; a1 = -4,  an = an-1 + 7  but you are the arithmetic sequence the first terme is ; a1 = -4  and common difference : r = 7
the general term is = an = a 1 + (n-1) r
an = -4 +7(n-1)
an = 7n -11 ....(**).....calculate