Question

which term of an AP 3.8.13.28

is 78​

Answer 1

Answer:

16

Step-by-step explanation:

This is an AP. nth term of AP is given by a + ( n - 1 )d, where symbols have their usual meanings.

Here,  

 a = first term = 3

 d = comm. diff. = 8 - 3 = 5

Let the required number of terms be n.

⇒ 78 = 3 + ( n - 1 )5

⇒ 78 - 3 = ( n - 1 )5

⇒ 75 = ( n - 1 ) 5

⇒ 75/5 = 15 = n - 1

⇒ 15 + 1 = n

⇒  16 = n

   Hence the required number of terms is 16

Answer 2

Answer:

here :Given first term(a)=3 and common difference =8-3=5 and tn=78

tn=a+(n-1)d

78=3+(n-1)5

78=3+5n-5

78=5n-2

78+2=5n

80=5n

n=16th term will be 78