Find a_ 30 - a_ 20 for the A.P. -9, -14, -19, -24, ..... - Vidyadip

Question

Find $a_{30} - a_{20}$ for the $A.P.$
$-9, -14, -19, -24, .....$

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Answer

Given,
$a_{30} - a_{20} = a + (30 - 1)d - (a + (20 - 1)d)$
($\therefore$$ a_n = a + (n - 1)d)$
$= a + 29d - a - 19d$
$= 10d$
$-9, -14, -19, -24, ....$
Common differecne (d) = Secomd term - First term
$= -14 - (-9)$
$= -14 + 9$
$d = -5$
Then $a_{30} - a_{20} = 10d$
$= 10 \times (-5)$
$= -50$

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