Question

How many terms of an A.P. 63,60,57,... taken so that their sum is 693?​

Answer 1

Answer:

3

Step-by-step explanation:

a=63 d=(-3)

sum of n terms=n/2(2a+(n-1)d)

693=n/2(2×63+3n-3)

1386=3n^2+123n

divide equation by 3

462=n^2+41n

n^2+41n-462=0

n^2-3n+44n-462=0

n(n-3)+44(n-3)=0

(n+44)(n-3)=0

n=3or(-44)

since n is no. of terms it can't be negative so,

n=3