Hello : (-6a)-(-3a) =(-3a)-(0) = (0)-(3a) = (3a)-(6a) = -3a (arthmetic<span> sequence, the common - diff is : d= -3a the first term is : U1 = 6a </span><span>a general rule for the n th term is : Un =U1+(n-1)d Un = 6a +(n-1)(-3a) = Un = 6a -3an+3a </span>Un = -3an +9a
