Question

Q5. In an A.P., if d = -2.n=8, nth term 1pc
= 4, then the value of first term is:
O 20
O 28
O
18
O
42​

Answer 1

Answer:

Let S

n

​

be the sum of n terms of an AP with first term a and common difference d.

Since S

n

​

=3n

2

−n and d=6

⇒S

n

​

=

2

n

​

(2a+(n−1)d)=3n

2

−n

2

n

​

(2a+(n−1)6)=3n

2

−n

n(a+(n−1)3)=3n

2

−n

(a+3n−3)=3n−1

a=2

Step-by-step explanation:

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Answer 2

Answer:

2

Step-by-step explanation:

Let S

n

be the sum of n terms of an AP with first term a and common difference d.

Since S

n

=3n

2

−n and d=6

⇒S

n

=

2

n

(2a+(n−1)d)=3n

2

−n

2

n

(2a+(n−1)6)=3n

2

−n

n(a+(n−1)3)=3n

2

−n

(a+3n−3)=3n−1

a=2