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