Maths / Arithmetic Progression / Sum of First n Terms

QUESTION

If $\dpi{120} \fn_jvn \large n^t^h$ term of an AP is 5 + 2n, find the sum of the first 20 terms of the AP.

EXPLANATION
Explain TypeExplanation Content
Text

$\dpi{100} a_n$ = 5 + 2n

$\dpi{100} a_1$ = 5 + 2 = 7

$\dpi{100} a_2$ = 5 + 2 X 2 = 9

d = $\dpi{100} a_2$ - $\dpi{100} a_1$ = 9 - 7 = 2

$\dpi{100} S_2_0$ = 10[14 + 19 x 2]

= 10(14 + 38) = 520

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