Question

If sin42 degrees = 2/3 then cos48 degrees = what? If tan20.5= 3/8, the tan69.5= what?

Answer 1

Big ifs, question writers. These are of course approximations.

The "co" in cosine comes from complementary angles. It means since

$42^\circ + 48 ^\circ = 90^\circ$

$\sin 42^\circ = \cos 48^\circ$

Answer: cos 48° = 2/3

Similarly,

$20.5^\circ +69.5^\circ = 90^\circ$

$\tan 69.5^\circ = \cot 20.5^\circ = \dfrac{1}{\tan 20.5^\circ} = \dfrac 8 3$

Answer: tan 69.5° = 8/3