A) 13
B) 15
C) 29
D) 18
Correct Answer: B
Solution :
\[\sqrt{3}[1+\sqrt{25}+\sqrt{81}+\sqrt{69}+......]=435\sqrt{3}\] \[\sqrt{3}[1+5+9+13+.....{{T}_{n}}]=435\sqrt{3}\] \[=\sqrt{3}\times \frac{n}{2}[2+(n-1)4]=435\sqrt{3}\] \[2n+4{{n}^{2}}-4n=870\] \[=4{{n}^{2}}-2n-870=0\] \[=2{{n}^{2}}-n-435=0\] \[n=\frac{1\pm \sqrt{1+4\times 2\times 435}}{4}\] \[=\frac{1\pm 59}{4}\] \[=\frac{1+59}{4}=4;\frac{1-59}{4}\]
You need to login to perform this action.
You will be redirected in
3 sec
