If all the angles are 60 degrees, this is an equilateral triangle. This means that all the sides have the same lengths. Whatever length side a is, b and c have the same length.
Hope this helps :)
The geometric sequence is given by:
an=ar^(n-1)
where:
a=first term
r=common ratio
n is the nth term
given that a=4, and second term is -12, then
r=-12/4=-3
hence the formula for this case will be:
an=4(-3)^(n-1)
where n≥1
