How to calculate the common difference when the first term and the nth term is know. Question: The 28th term of an AP is -5. Find the common difference if its first term is 31. Solution T1 = a ( First term of the sequence) a = 31 T28 = -5 (28th term of the sequence) d = ? (common difference) Recall the nth term formula of Ap i.e Tn = a + (n-1)d Substitute 28 for n to get the following equation T28 = a + (28-1)d T28 = a + 27d Substitute T28 for -5 and 31 for a in the equation above -5 = 31 + 27d Subtract 31 from both sides of the equation -5 -31 = 27d -36 = 27d Divide through by 27 -36/27 = 27d/27 ...
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