Question

what is the common difference of an ap in which
$a21 - a7 = 84$
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Answer 1

Step-by-step explanation:

see the image u willl understand thank

fellow brainly user...

Answer 2

$\bold{Given:-} \begin{cases} \sf{Given \: \: AP:-} \\ \sf{ a_{21}-a_7=84.} \end{cases}$

$\large \underline\bold{Solution:-}$

$Let \: first \: term \: be \: a \: and \: common \: difference \: be \: d$

$\implies a_{21}-a_7=84. \\ \\ \implies( a + 20d) - (a + 6d) = 84. \\ \\ \implies \cancel a + 20d- \cancel a - 6d = 84. \\ \\ \implies 14d = 84. \\ \\ \implies d = \frac{ \cancel{84}}{ \cancel{14}} . \\ \\ \implies d = 6.$

$\purple{ \huge {\boxed{d = 6.}}}$