Question

the first and the last terms of an ap are 1 and 11 respectively if the sum of its terms is 36 find the number of terms

Answer 1

$\large\underline{ \underline{ \purple{ \bold{\mathrm{ANSWER}}}}}$

➥ There are 6 terms the AP.

$\large{\underline{\bf{\blue{Explanation:-}}}}$

Sum of n terms of an AP a, a + d , a + 2d ,.....etc .is given by the formula-

✰ $\bf\:s_n= \frac{n}{2}[2a+(n - 1)d]$

✰ $\bf\:s_n= \frac{n}{2}[a+a_n]$

$\large{\underline{\bf{\green{Given:-}}}}$

✰ First term of AP (a) = 1

✰ last term of ap (an) = 11

✰ Sum of all terms = 36

$\large{\underline{\bf{\green{To\:Find:-}}}}$

✰ We need to find the number of terms in AP.

$\huge{\underline{\bf{\red{Solution:-}}}}$

As we know,

$\bf\:s_n= \frac{n}{2}[a+a_n]$

Then , putting all values in the formula.

$:\implies\bf\:36= \frac{n}{2}[1+11]$

$:\implies\bf\:36= \frac{n}{2}[12]$

$: \implies\bf\:36= \dfrac{n}{ \cancel{2}} \times{ \cancel 12}$

$:\implies\bf\:36= 6n$

$:\implies\bf\:n= \cancel\dfrac{36}{6}$

$:\implies\bf\:n= 6$

So there are 6 terms in the AP.

━━━━━━━━━━━━━━━━━━━━━━━━━

Answer 2

Answer:

Explanation:

Sorry, but can you please explain your question

Because i am not able to understand

I hope you will understand my problem

Please mark me as brainlist.

Please give me thankso