Q31 / 54 · JEE Advanced 2018 (Paper 1) · Mathematics

Let a, b, c be three non-zero real numbers such that the equation 3acos⁡x+2bsin⁡x=c, x∈-π2, π2 has two distinct real roots α and β with α+β=π3. Then, the value of ba is

Correct answer: 0.5

Solution

3cos⁡x+2basin⁡x=ca
Now, 3cos⁡α+2basin⁡α=ca …i   
3cos⁡β+2basin⁡β=ca …ii 

From equations i and ii

⇒3cos⁡α-cos⁡β+2basin⁡α-sin⁡β=0
⇒3-2sin⁡α+β2sin⁡α-β2+2ba2cos⁡α+β2sin⁡α-β2=0

⇒-3+23·ba=0
⇒ba=12=0.5

Hence, the correct answer is 0.5.

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