Answer :

False

cos2 23° - sin2 67° =(cos 23°+sin 67°)(cos 23°-sin 67°)


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


= [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°+cos 23°).0


= 0, which is neither positive nor negative


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