Question

sum of a certain number of terms of an AP series -8, -6, –4, is 52. The number of terms is (a) 12 (b) 13 (c) 11 (d) none of these​

Answer 1

Answer:

13

Step-by-step explanation:

a=-8

d=2

sn=52

Sn=n/2{2a+[n-1]d}

52=n/2{2*-8+[n-1]2}

    =n/2{-16+2n-2}

    =n/2{-18+2n}

    =-9n+nsquare

nsquare-9n-52=0

nsquare-13n+4n-52=0

n[n-13]+4[n-13]=0

n=-4 or n=13

n=-4 is invalid

therefore n=13.

I hope this helps you

Answer 2

Answer:

(b) 13

Step-by-step explanation:

AP: -8,-6,4....

Sn = 52

d = -6+8 = 2

so, 52 = n/2[2×(-8)+(n-1)2]

52 = n[-8+n-1]

52 = n²-9n

n²-9n-52 = 0

n²-13n+4n-52 = 0

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

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

so,, n = 13 ....ans.

option b is correct.