To check -150 is present in the sequence -150=a+(n-1)d According to the given series a=11,d=-3 So we need to find n If n is a fraction then it does not belongs to that series From formula=-150=11+(n-1)-3 -150=11-3n+3 -150=14-3n -150-14=-3n -164=-3n n=164/3 We got n as a fraction so -150 does not belong to series
