Question
Question: Positive value of n satisfying 2 + (6.2<sup>2</sup> – 4.2) \+ (6.3<sup>2</sup> – 4.3) + ......... +...
Positive value of n satisfying 2 + (6.22 – 4.2)
+ (6.32 – 4.3) + ......... + (6.n2 – 4.n) = 140 is –
A
3
B
4
C
5
D
None of these
Answer
4
Explanation
Solution
2 + 6(22 + 32 + 42 ....+ n2) – 4(2 + 3 + 4 ....+ n) = 140
Solving n = 4