Question

Sn= 4n^2 - 5n, find an

Answer 1

Answer:

s1=4-5= -1

s2=16-10=6

S3=36-15=21

S4=64-20=44

we know Sn= (n/2) [2a+(n-1)d] where a is 1st term

d is common difference

and n is no of terms

S1=1 implies 1/2 [2a +0]= -1

So, a= -1

S2= (2/2) [2 * -1 + 1*d]=6

So, d= 8

The series will be -1, 7, 15, 23,....

Now we can find Tn= a + (n-1)*d