Question

how many terms of the arithmetic progression 24 , 21, 18 most be taken so that their sum in 78 video​

Answer 1

Answer:

ok suno

Step-by-step explanation:

its an arithenatic progression

so the difference here is 3 and apply the formula

A=

Answer 2

Answer:

either 4 or 13 terms

Step-by-step

Let the no. of terms required be n

The given AP is 24,21,18,...

S= $\frac{n}{2} [ 2a + (n-1)d ]$

78 = $\frac{n}{2} [2(24) + (n-1)-3]$

78 = $\frac{n}{2} [ 48 -3n + 3 ]$

156 = n [51 -3n]

$3n^{2} - 51n + 156$ = 0

$n^{2} -17n +52 =0$                               [ whole equation divided by 3]

$n^{2} -13n - 4n + 52$

n ( n - 13 ) - 4 ( n - 13 ) = 0

( n - 13 ) ( n - 4 ) = 0

n - 13 = 0          n - 4 = 0

n = 13       0r     n = 4