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Question

If $\sin(x) = 0.6$ and $x \in (0, \pi/2)$, find $\sin(2x) + \cos(2x)$.

This question was previously asked in
SSC CGL 2025 Tier 1 Question Paper (25-Sep-2025) (Shift 3)
The correct answer is
1.24

We are given that $\sin(x) = 0.6$ and $x$ is in the first quadrant ($x \in (0, \pi/2)$). We need to find the value of $\sin(2x) + \cos(2x)$.

Find Cosine Value

First, find $\cos(x)$ using the Pythagorean identity $\sin^2(x) + \cos^2(x) = 1$. Since $x$ is in the first quadrant, $\cos(x)$ is positive.

  1. Calculate $\cos^2(x)$: $ \cos^2(x) = 1 - \sin^2(x) $ $ \cos^2(x) = 1 - (0.6)^2 = 1 - 0.36 = 0.64 $
  2. Find $\cos(x)$: $ \cos(x) = \sqrt{0.64} = 0.8 $

Calculate Double Angle Values

Now, use the double angle formulas to find $\sin(2x)$ and $\cos(2x)$.

  • Calculate $\sin(2x)$: $ \sin(2x) = 2 \sin(x) \cos(x) $ $ \sin(2x) = 2 \times (0.6) \times (0.8) = 2 \times 0.48 = 0.96 $
  • Calculate $\cos(2x)$: $ \cos(2x) = \cos^2(x) - \sin^2(x) $ $ \cos(2x) = (0.8)^2 - (0.6)^2 = 0.64 - 0.36 = 0.28 $

Compute Final Expression

Finally, add the values of $\sin(2x)$ and $\cos(2x)$:

$ \sin(2x) + \cos(2x) = 0.96 + 0.28 = 1.24 $

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