If the sin θ = 9 5 √ 10 , what is the cos θ ?

Question

I don't understand what I'm supposed to do to find the answer to this question

Answer 1

Whatever the value of the sine is (and you have not made that clear yet), you can solve for cosine's value based on understanding of the fundamental Pythagorean identity, which is that the sum of the squares of sine and cosine always equals 1.  When you solve for cosine, you'll get "plus or minus" and that decision must be based on what quadrant(s) are involved.