Multiple choice

If cos (40° + x) = sin 30°, find the value of x.

  1. 60°

  2. 20°

  3. 30°

  4. 90°
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

cos (40° + x) = sin 30˚ = cos 60° 40° + x = 60°   x = 20°

AI explanation

Since sin 30° = cos 60° (co-function identity, sinθ = cos(90°–θ)), the equation cos(40°+x) = sin 30° becomes cos(40°+x) = cos 60°. Equating the angles gives 40°+x = 60°, so x = 20°.

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