Medium
In an AP, the first term is 9 and the common difference is -6. Which term of the AP is -21?
Explanation
Explanation
Using aₙ = a + (n-1)d, set a + (n-1)d = -21: 9 + (n-1)(-6) = -21. Solving, (n-1) = (-21 - 9)/-6 = 5, so n = 6. Thus -21 is the 6th term.
PRO TIP
Re-check your working by substituting the answer back into the original question.