Respuesta :

Answer:

cos(X+Y) = cos(55+35) = cos(90) = 0

Step-by-step explanation:

cos(X+Y) = cosXcosY - sinXsinY

cos(55+35) = cos(55)cos(35) - sin(55)sin(35)

cos(55+35) = cos(55)cos(35) - cos(90-55)cos(90-35)

cos(55+35) = cos(55)cos(35) - cos(35)cos(55)

cos(55+35) = 0

cos(90) = 0