Question

 Write True' or False' and justify your answer  the following : 

The value of  \[\cos^2 23 - \sin^2 67\]  is positive . 

Answer 1

\[\cos^2 23°- \sin^2 67°\]
\[ = \sin^2 \left( 90°- 23°\right) - \sin^2 67°\]
\[ = \sin^2 67° - \sin^2 67°\]
\[ = 0\] 

Which is not positive, the given statement is false.