Hey there! I'm happy to help!
There is a rule in trigonometry that says that the sine of one angle is equal to the cosine of that angle's complement.
Complementary angles are ones that equal 90 degrees when added.
We see that L and M are complementary angles, so we can apply this rule.
The sine of L is 19/20. We know that the sine of angle L is equal to the cosine of L's complement from our rule, which is M. This means that the cosine of M is equal to 19/20.
Have a wonderful day!
