JIPMAT 2021 (QA) - The minimum value of (2 ^2 + 3 ^2) is | PYQs + Solutions | AfterBoards
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JIPMAT 2021 (QA) PYQs

JIPMAT 2021

Geometry
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Trigonometry

Conceptual

The minimum value of (2sin2θ+3cos2θ)(2 \sin^2\theta + 3 \cos^2\theta) is

Correct Option: 3
1) Given expression: 2sin2θ+3cos2θ2\sin^2 \theta + 3\cos^2 \theta
2) Using identity sin2θ+cos2θ=1\sin^2 \theta + \cos^2 \theta = 1:\newline Therefore, sin2θ=1cos2θ\sin^2 \theta = 1 - \cos^2 \theta
3) Substituting:\newline 2(1cos2θ)+3cos2θ2(1 - \cos^2 \theta) + 3\cos^2 \theta\newline =22cos2θ+3cos2θ= 2 - 2\cos^2 \theta + 3\cos^2 \theta\newline =2+cos2θ= 2 + \cos^2 \theta
4) Since cos2θ\cos^2 \theta varies between 0 and 1:\newline - When cos2θ=0\cos^2 \theta = 0, expression = 2\newline - When cos2θ=1\cos^2 \theta = 1, expression = 3
5) Therefore:\newline Minimum value = 2 (when cos2θ=0\cos^2 \theta = 0)\newline Maximum value = 3 (when cos2θ=1\cos^2 \theta = 1)
The minimum value is 2.

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