A question in my math sheet asks to find "Cos 75 °"
We're on the unit of Compound Angle Formulae too. I was just wondering is it simply pressing cos 75 on the calculator or do I have to apply anything else to it? Thanks!
Pressing cos(75deg) on the calculator is the easiest way.
But that's not the way you're asked to do. You are asked to do it using trigonometry.
You are on compound angles formulae, so that is the way you are supposed to do.
cos(75deg)
= cos(30deg +45deg)
= cos(30deg)cos(45deg) -sin(30deg)sin(45deg)
= [(sqrt(3) /2)*(1 / sqrt(2))] -(1/2)(1 / sqrt(2))
= [sqrt(3) / 2sqrt(2)] -[1 / 2sqrt(2)]
= [sqrt(3) -1] / [2sqrt(2)]
= [sqrt(6) -sqrt(2)] / 4
= 0.258819045 -------------------answer.