Which term of the A.P: 21,18,15,....is -81? Also,is any term 0?

1.	Which term of the A.P: 21,18,15,....is -81? Also,is any term 0?
Answer» 8th term is 0 An=a+(n-1)d-81=21+(n-1)-3-81-21=(n-1)-3-102=(n-1)-3-102÷-3=n-134=n-134+1=n35=n

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