Question

tan48 tan 16 tan 42 tan 74 = 1
show that
cos 36 cos 54 _ sin 36 sin 54 =0
show that

solve this with solution.
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Answer 1

cos 11°. 2) sin 0°. 3) cos 13°. 4) cos 24°. 5) tan 75°. 6) tan 15°. 7) tan 54°. 8) tan 2° .... 8) tan 36° 9) tan 74° 10) tan 15° 11) tan 53° 12) sin 26° 13) sin 37° 14) cos 49° 15 ...
I hope it is correct

Answer 2

Hi we know
$\cos( \alpha + \beta ) = \cos( \alpha ) \cos( \beta ) - \sin( \alpha ) \sin( \beta )$
Therefore
$\cos(36) \cos(54) - \sin(36) \sin(54) = \cos(36 + 54) = \cos(90) = 0$
I don't why the first hint is given.
Hope this helps.