Which term of the AP 21,18,15,......is …
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Posted by Sachin Gothi Patidar 1 year, 11 months ago
- 1 answers
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Preeti Dabral 1 year, 11 months ago
Here the given AP is : 21,18,15,--------
Here a=21 and d=18-21=-3,an=-81
{tex}\mathrm{We}\;\mathrm{know}\;\mathrm{that}\;{\mathrm a}_{\mathrm n}=\mathrm a+(\mathrm n-1)\mathrm d{/tex}
{tex}\Rightarrow{/tex} -81=21+(n-1)(-3)
{tex}\Rightarrow{/tex} -81=21-3n+3
3n = 81+21+3=105
So n = {tex}\frac{105}{3}{/tex} = 35
So, -81 is the 35th term of this AP
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