Question

The first term of an A.P. is 5 and the common difference is 4. Find the sum of first 12 terms of the A.P. and also 19th term.​

Answer 1

Answer:

Step-by-step explanation:

Below in bold.

Step-by-step explanation:

Sum of n terms:

Sn = n/2[2a + (n-1)d]  where a = first term and d = common difference, so:

S12 =  12/2[2*5 + (12-1)*4]

= 6 * 54

= 324.

19th term

= a + (19-1)d

= 5 + 18*4

= 77.