Question

nth term of an ap is 4n-3 what is the sum of its first two terms​

Answer 1

an=4n-3

a1 =4×1-3

=4-3=1

a2=4×2-3

=8-3=5

a3=4×3-3

=12-3=9

AP is 1,5,9..........

S2= n/2(1+5)

=2/2(1+5)

=6

sum of its first two terms is 6.

Answer 2

• Details on AP (Arithmetic Progression) :

A progression a, b, c, d is said to be in AP when

    b - a = c - b = d - c

Taking the 1st two terms, we get

  b - a = c - b

  ⇒ b + b = c + a

  ⇒ 2b = c + a

  ⇒ b = $\frac{c+a}{2}$ , which is the value of the middle term of an AP with first three terms a, b, c

• Solution of the question :

The nth term of the AP is (4n - 3)

So, the 1st term = 4 (1) - 3 = 4 - 3 = 1

and the 2nd term = 4 (2) - 3 = 8 - 3 = 5

Hence, the required sum of first two terms

= 1 + 5 = 6