3 Answers

rakesh05's profile pic

rakesh05 | High School Teacher | (Level 1) Assistant Educator

Posted on

We know that cosAcosB-sinAsinB=cos(A+B)


                                    =cos90  (If The angle given is in degree)


mariloucortez's profile pic

mariloucortez | High School Teacher | (Level 3) Adjunct Educator

Posted on

Im not sure about your question here. If you need to simplify, you can just use your calculator and input cos(75)cos(15)-sin(75)sin(15) and press =.

You will be getting zero (0).

There is and identity for `cos(75)cos(15)-sin(75)sin(15)` .

Recall `cos(A+B) = cosAcosB - sinAsinB.`

Simply, A = 75 and B = 15.

So cos(75+15) = cos(90) = 0.

Therefore, the answer is 0.