By Mansi Yadav

Verified by Ajay Kumar

If \(\sin\theta-\cos\theta=\frac45\), then find the value of \(\sin\theta+\cos\theta\).

  1. \(\frac{\sqrt{34}}{5}\)

  2. \(\frac{5}{\sqrt{34}}\)

  3. \(\frac{\sqrt{24}}{5}\)

  4. \(\frac{5}{\sqrt{24}}\)

Answer: A

Solution

Solution: Use \((\sin\theta+\cos\theta)^2+(\sin\theta-\cos\theta)^2=2\). Thus, \((\sin\theta+\cos\theta)^2=2-\frac{16}{25}=\frac{34}{25}\). Taking the positive value given in the options, \(\sin\theta+\cos\theta=\frac{\sqrt{34}}5\). Trick: Square the sum and difference; their squares add up to 2.

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