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# Choose the correct answer from the given four options:

The $ 21^{\text {st }} $ term of the AP whose first two terms are $ -3 $ and 4 is

**(A)** 17

**(B)** 137

**(C)** 143

**(D)** $ -143 $

**Given: **

First two terms of the A.P. are $–3$ and $4$.

**To do:**

We have to find the $21^{st}$ term of the A.P.

**Solution:**

$-3,\ 4,\ 11,\ 18\ .......$

Here, first term $a=-3$

Common difference, $D=7$

$n=21$

Now, $A_n=a+( n-1)d$

$\Rightarrow a_{21}=-3+20\times( 7)$

$\Rightarrow a_{21}=-3+140$

$\Rightarrow a_{21}=137$

Hence the $21^{st}$ term of the A.P. is $137$.

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