1.

How many terms are there in the AP 7, 11, 15, …, 139 ?

Answer»

Given AP is 7, 11, 15, …., 139. 

First term of AP is a = 7. 

And common difference of AP is d = a2 – a1 = 11 – 7 = 4. 

Let nth term of AP is 139. 

∴ a + (n – 1) d = 139. (∵ nth term of AP is given by an = a + (n – 1) d) 

⇒ 7 + (n – 1)4 = 139 (∵ a = 7 & d = 4) 

⇒ 4(n – 1) = 139 – 7 = 132 

⇒ n – 1 = 132 4 = 33 

⇒ n = 33 + 1 = 34. 

Hence, total term in given AP is 34.



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