Question

find 20th term of an A.P 21,16,11,6_ _​

Answer 1

Given:–

• A.P = 21, 16, 11, 6.....

To Find:–

• What is the 20th term ?

Solution:–

Let the 20th term of an A.P be $\sf{{a}_{20}}$

❍ d = a2 – a1 = 16 – 21

❍ d = –5

As we know that, formula for $\sf{a_n}$ term is:-

${\Large{\underbrace{\overbrace{\bf{a_n = a + (n-1)d}}}}}$

A/c

$\dashrightarrow{\sf {a}_{20} = 21 + (20-1)-5}$

$\dashrightarrow{\sf {a}_{20} = 21 + 19 \times -5}$

$\dashrightarrow{\sf {a}_{20} = 21 -95}$

$\dashrightarrow{\bf \: {a}_{20} = -74 \: \star}$

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