Question

the nth term of an A.P is given by an =7-3n then the common difference is _____​

Answer 1

Step-by-step explanation:

In the given problem, nth term is given by, an = 3n + 7. To find the common difference of the A.P., we need two consecutive terms of the A.P. So, let us find the first and the second term of the given A.P. Therefore, the common difference is d = 3 .

Answer 2

Answer:

Let first term of AP be, a

Common difference be d

According to question,

nth term is => 7−3n=a+(n−1)d

=> a+nd−d=7−3n

By comparing coefficents, we get

a=4 & d=−3

So, sum first 25 terms,

2

n

[2a+(n−1)d]

=>

2

25

[2×4+(25−1)(−3)]

=>

2

25

[8−72]

=> −400