How do you simplify sec(x+y)cos(x+y) to trigonometric functions of x and y?

1 Answer

sec(x+y)cos(x+y)=(sinxcosy+cosxsiny)2cosxcosysinxsiny

Explanation:

Do a little transformation

sec(x+y)cos(x+y)

1cos(x+y)cos(x+y)

Use the LCD cos(x+y)

1cos2(x+y)cos(x+y)

From Pythagorean Relation

sin2(x+y)=1cos2(x+y)

so that

1cos2(x+y)cos(x+y)

sin2(x+y)cos(x+y)

From Sum and Difference Formulas

(sinxcosy+cosxsiny)2cosxcosysinxsiny

have a nice day!