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Question
t19 = ? for the given A.P., 9, 4, −1, −6 ........
Activity :- Here a = 9, d = `square`
tn = a + (n − 1)d
t19 = 9 + (19 − 1) `square`
= 9 + `square`
= `square`
Solution
Here a = 9, d = 4 - 9 = − 5
tn = a + (n − 1)d
t19 = 9 + (19 − 1) − 5
= 9 + 18(-5)
= 9 + − 90
= − 81
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