Question:

If \[ \sin\theta+\cos\theta=\sqrt2 \] then \[ \sin\theta\cos\theta= \]

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Whenever \((\sin\theta+\cos\theta)\) is given, squaring helps apply the identity \(\sin^2\theta+\cos^2\theta=1\).
Updated On: Jul 15, 2026
  • \(2\)
  • \(\frac12\)
  • \(2\sqrt2\)
  • \(\frac13\)
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The Correct Option is B

Solution and Explanation

Square both sides: \[ (\sin\theta+\cos\theta)^2=2 \] Expand: \[ \sin^2\theta+\cos^2\theta+2\sin\theta\cos\theta=2 \] Using identity: \[ \sin^2\theta+\cos^2\theta=1 \] So: \[ 1+2\sin\theta\cos\theta=2 \] \[ 2\sin\theta\cos\theta=1 \] \[ \sin\theta\cos\theta=\frac12 \] Thus, \[ \boxed{\frac12} \]
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