Question

Write an explicit formula for the sequence 7, 1, -5, -11, -17,... Then find a14

Answer 1

An=a1+d (n-1)
a1= 7
find d
Let's use a2
a2=1
1=7+d (2-1)
1=7+d
-7 both sides
d=-6
explicit formula is

an=7+-6 (n-1)

a14=?
a14=7-6 (14-1)
a14=7-6×13
a14=7-78
a14=-71