Question 22
The numbers $$1,3,6,10,\ldots$$ are called triangular numbers. The $$n$$th triangular number is $$T_n=\frac{n(n+1)}{2}$$. Then the value of $$T_{3n+1}-9T_n$$ is equal to
Correct Answer: 1
Solution
We have $$T_{3n+1}=\frac{(3n+1)(3n+2)}{2}$$ and $$9T_n=\frac{9n(n+1)}{2}$$. Their difference is $$\frac{9n^2+9n+2-9n^2-9n}{2}=1$$.
Get AI Help
Book Free CAT Mentorship
Get personalized CAT strategy from a 99%iler
500+ students mentored
OTP Verification
Enter the 6-digit code sent to your phone
Booking Summary
Session:Free CAT Mentorship
Phone:
Date:
Time:
Enter OTP
Didn't receive the OTP?
