Question

find the sum of first 20 terms of the A.P 1,4,7......​

Answer 1

Answer:

here is u r answer

Step-by-step explanation:

n= 20

a= 1

d= 3

SN=n/2(2a+(n-1)d

Answer 2

$\large\fbox\textit{\green{Gɪᴠᴇɴ :}}$

${ \mathtt{\blue{a = 1}}} \\ { \mathtt{\blue{d = a _{2} - a _{1} = 4 - 1 = 3 }}} \\ { \mathtt{\blue{n = 20}}}$

$\large\fbox\textit{\green{Tᴏ Fɪɴᴅ :}}$

${ \mathtt{\blue{sum \: of \: 20 \: terms \: =s _{20} = </p><p> \: ? }}}$

$\large\fbox\textit{\green{Aɴsᴡᴇʀ}}$

${ \mathtt{\blue{s _{n} = \frac{n}{2} \: (2a + (n - 1)d) }}} \\ { \mathtt{\blue{s _{20} = \frac{20}{2} (2 + (20 - 1)3)}}} \\ { \mathtt{\blue{s _{20} = 10(2 + (19)3) }}} \\ { \mathtt{\blue{s_{20} = 10(2 + 57) }}} \\ { \mathtt{\blue{s_{20} = 10(59)}}} \\ { \boxed {\sf\mathtt{ \underline\blue{s _{20} = 590}}}}$