Question

If the sum and product of the first three term in an A.P are $33$ and $1155$ respectively, then a value of its 11th term is:

• A. $-25$
• B. $25$
• C. $-36$
• D. $-35$

Answer 1

The correct option is A $-25$

$a-d+a+a+d=33\Rightarrow a=11$

$a(a^2-d^2)=1155$

$121-d^2=105$

$d^2=16\Rightarrow d=\pm 4$

If $d=4$ then 1st term $=7$

If $d=-4$ then 1st term $=15$

$T_{11}=7+40=47$

OR $T_{11}=15-40=-25$