Question

Evaluate cos^2 23 - sin^2 67​

Answer 1

Answer:

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Answer 2

Step-by-step explanation:

Since, (a2-b2) = (a+b)(a-b)

cos2 23° – sin2 67°

=(cos 23°+sin 67°)(cos 23°-sin 67°)

= [cos 23°+sin(90°-23°)] [cos 23°-sin(90°-23°)]

= (cos 23°+cos 23°)(cos 23°-cos 23°)

(∵sin(90°-θ) = cos θ)

= (cos 23°+cos23°).0

=0

cos^2 23 - sin^2 67 =0