Question

What is the value of (cos² 67° – sin² 23°)?

Answer 1

`cos^2 67^@ - sin^2 23^@`

`= cos^2 67^@ - sin^2 (90^@ - 67^@)`

`= cos^2 67^@ - cos^2 (67^@)`    `(∵ sin^2 (90 - theta ) = cos^2 theta)`

= 0