NIMCET 2009 — Mathematics PYQ
NIMCET | Mathematics | 2009If tan−12x+tan−13x=4π, then x is:
Choose the correct answer:
- A.
61
(Correct Answer) - B.
31
- C.
21
61
Explanation
To find x, we apply the identity for the sum of two inverse tangents:
tan−1A+tan−1B=tan−1(1−ABA+B)
1. Equation Setup
Substituting A=2x and B=3x:
tan−1(1−(2x)(3x)2x+3x)=4π
1−6x25x=tan(4π)
2. Solving for x
Since tan(4π)=1:
1−6x25x=1
5x=1−6x2
6x2+5x−1=0
3. Factoring
6x2+6x−x−1=0
6x(x+1)−1(x+1)=0
(6x−1)(x+1)=0
4. Final Values
x=61 (Valid)
x=−1 (Rejected because it results in a negative value for the sum)
Correct Option:(a) 61
Explanation
To find x, we apply the identity for the sum of two inverse tangents:
tan−1A+tan−1B=tan−1(1−ABA+B)
1. Equation Setup
Substituting A=2x and B=3x:
tan−1(1−(2x)(3x)2x+3x)=4π
1−6x25x=tan(4π)
2. Solving for x
Since tan(4π)=1:
1−6x25x=1
5x=1−6x2
6x2+5x−1=0
3. Factoring
6x2+6x−x−1=0
6x(x+1)−1(x+1)=0
(6x−1)(x+1)=0
4. Final Values
x=61 (Valid)
x=−1 (Rejected because it results in a negative value for the sum)
Correct Option:(a) 61
