Question

Find the 21st term of AP whose first two terms are -3 and 4​

Answer 1

Answer :

21st term = 137

Step-by-step explanation :

Given :

In an A.P.,

• first term, a = -3
• second term, a₂ = 4

To find :

21st term of AP

Solution :

In an A.P., nth term is given by,

  $\underline{\boxed{\bf a_n=a+(n-1)d}}$

where

a denotes first term

d denotes common difference

In A.P., Common difference is the difference between a term and it's preceding term.

 d = a₂ - a

 d = 4 - (-3)

 d = 4 + 3

 d = 7

Substitute n = 21,

a₂₁ = a + (21 - 1)d

a₂₁ = -3 + 20(7)

a₂₁ = -3 + 140

a₂₁ = 137

∴ The 21st term of given A.P. is 137

Answer 2

$\large\underline{ \underline{ \sf \maltese{ \: Question⤵ }}}$

Find the 21st term of AP whose first two terms are -3 and 4.

❇ Solution ⬇

In an A.P., nth term is given by,

$\underline{\boxed{\bf a_n=a+(n-1)d}}$

where

a denotes first term

d denotes common difference

In A.P., Common difference is the difference between a term and it's preceding term.

 d = a₂ - a

 d = 4 - (-3)

 d = 4 + 3

 d = 7

Substitute n = 21,

a₂₁ = a + (21 - 1)d

a₂₁ = -3 + 20(7)

a₂₁ = -3 + 140

a₂₁ = 137

∴ The 21st term of given A.P. is 137

Thank you.