Question

solve this plz..need it urgently​

Answer 1

Answer:

12

Step-by-step explanation:

see tge attachment

there is explanation

Answer 2

$\red{\large {\underline{ \underline{ \star \: {Given:-}}}}}$

Q. Find the number of terms in the A.P :-

18 , 15 1/2 , 13 ...........-47.

$\red{\large {\underline{ \underline{ \star \: { To \: \: \: Find:-}}}}}$

${n}^{th} \: terms.$

$\red{\large {\underline{ \underline{ \star \: { Solution:-}}}}}$

$a = 18. \\ \\ d = \sf a_2 - a_1. \\ \\ \: \: \: = 15 \times \frac{1}{2} - 18. \\ \\ \: \: \: = \frac{31}{2} - 18. \\ \\ \: \: \: = \frac{31 - 36}{2} \\ \\ \: \: \: = - \frac{5}{2} .$

Here,

First number ( a ) and common difference ( d )

a = 18. and. d = -5/2.

Now,

Using formula ,

$\sf \: a_n = a + (n - 1)d \\ \\ - 47 = 18 + (n - 1) \frac{ - 5}{2} . \\ \\ - 47 = 18 - \frac{5}{2} n + \frac{5}{2} . \\ \\ - 47 = 18 + \frac{5}{2} - \frac{5}{2} n. \\ \\ - 47 = \frac{36 + 5}{2} - \frac{5}{2}n. \\ \\ - 47 = \frac{41}{2} - \frac{5}{2}n. \\ \\ \frac{ - 94 - 41}{2} = - \frac{5}{2} n. \\ \\ - \frac{135}{ \cancel2} = - \frac{5}{ \cancel2} n. \\ \\ 135 = 5n. \\ \\ n = \cancel\frac{135}{5} . \\ \\ n = 27.$

Hence,

$\huge \: n = 27.$