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Question
Write True' or False' and justify your answer the following :
The value of \[\cos^2 23 - \sin^2 67\] is positive .
Solution
\[\cos^2 23°- \sin^2 67°\]
\[ = \sin^2 \left( 90°- 23°\right) - \sin^2 67°\]
\[ = \sin^2 67° - \sin^2 67°\]
\[ = 0\]
Which is not positive, the given statement is false.
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