Question #ff2fc

1 Answer
Aug 31, 2016

" The Reqd. Sum"=580/9~~64.44 The Reqd. Sum=580964.44.

Explanation:

Let the A.P. be,

a,a+d,a+2d,a+3d,..., "where", a,d, in RR, and, d!=0.

Let t_n, and, S_n be the n^(th) term, &, the sum of first n

terms of A.P. resp.

We know that, t_n=a+(n-1)d, and, S_n=n/2[2a+(n-1)d].

t_3:t_6=9:4 ...."[Given]"rArr (a+2d)/(a+5d)=9/4...........(1)

Further, "Given "S_5=60 rArr 5/2(2a+4d)=60, or, (a+2d)=12.

By (1)," then, "a+5d=(4*12)/9=16/3

Therefore, (a+2d)-(a+5d)=12-16/3 rArr -3d=20/3 rArr d=-20/9.

Since, a+2d=12, we have,

a=12-2(-20/9)=12+40/9=148/9.

Finally, the Reqd. Sum =S_10=10/2(2a+9d)

=5[2*148/9+9(-20/9)]

=5[296/9-180/9]

=(5*116)/9

=580/9~~64.44.

Enjoy Maths.!