JIPMAT 2024 (QA) - If + =sqrt(7)2, then ( - ) is equal to : | PYQs + Solutions | AfterBoards
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JIPMAT 2024 (QA) PYQs

JIPMAT 2024

Geometry
>
Trigonometry

Hard

If sinθ+cosθ=72\sin \theta+\cos \theta=\frac{\sqrt{7}}{2}, then (sinθcosθ)(\sin \theta-\cos \theta) is equal to :

Correct Option: 2
1) Given: sinθ+cosθ=72\sin \theta + \cos \theta = \frac{\sqrt{7}}{2}
2) Let's square this equation:
(sinθ+cosθ)2=74(\sin \theta + \cos \theta)^2 = \frac{7}{4}
sin2θ+2sinθcosθ+cos2θ=74\sin^2 \theta + 2\sin \theta\cos \theta + \cos^2 \theta = \frac{7}{4}
Since sin2θ+cos2θ=1\sin^2 \theta + \cos^2 \theta = 1:
1+2sinθcosθ=741 + 2\sin \theta\cos \theta = \frac{7}{4}
2sinθcosθ=342\sin \theta\cos \theta = \frac{3}{4} ...(1)
3) Now for sinθcosθ\sin \theta - \cos \theta, let's square: \newline (sinθcosθ)2(\sin \theta - \cos \theta)^2
=sin2θ2sinθcosθ+cos2θ= \sin^2 \theta - 2\sin \theta\cos \theta + \cos^2 \theta
=12sinθcosθ= 1 - 2\sin \theta\cos \theta
4) From equation (1): \newline (sinθcosθ)2(\sin \theta - \cos \theta)^2
=134= 1 - \frac{3}{4}
=14= \frac{1}{4}
5) Therefore: \newline sinθcosθ=±12\sin \theta - \cos \theta = \pm\frac{1}{2}
6) Since sinθ+cosθ=72\sin \theta + \cos \theta = \frac{\sqrt{7}}{2} is positive,
sinθcosθ=12\sin \theta - \cos \theta = \frac{1}{2}

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