Question

If a=12,d=7,n=15 find

Answer 1

Heya,

Pls mention your questions clearly..,

Anyways here is your answer ,

a n = a + (n-1) d
= 12 + (7-1)15
= 12 + 6(15)
= 12 + 90
= 102


S n = n/2 (a + a n )
= 15/2 (12+102)
= 7.5 (114)
= 855

Hope this is what you
asked for ..

Hope it’ll help !! ♥️

Answer 2

Answer:

15th term of an A.P = 110

Sum of first 15 terms of an A.P = 840

Step-by-step explanation:

Given,

a = 12

d = 7

n = 15

How To Do :-

Here they given the values of 'first term(a) , common difference(d) , n'. So if we observed the question clearly we may get dóubt that wether they are asked us to find the value of 'nth term or sum of first 'n' terms. So let's find both the values.

To Find :-

1) 15th term of an A.P

2) Sum of first 15 terms of an A.P

Formula Required :-

nth term of an A.P :-

a_n = a + (n - 1)d

Sum of first 'n' terms of an A.P :-

S_n = n/2 [2a + (n - 1)d]

Solution :-

15th term of an A.P :-

a_15 = a + (15 - 1)d

= a + 14d

Substituting the values :-

= 12 + 14(7)

= 12 + 98

= 110

15th term of an A.P = 110.

Sum of first 15 terms of an A.P :-

S_n = 15/2 [ 2a + (15 - 1)d ]

= 15/2 [ 2a + 14d ]

Substituting the values :-

= 15/2 [ 2(12) + 14(7) ]

= 15/2 [ 14 + 98 ]

= 15/2 [ 112 ]

= 15(56)

= 840

Sum of first 15 terms of an A.P = 840.