Trigonometric Sum Difference Formula

Write the following expression as the sine, cosine, or tangent of an angle.
cos(175)cos(55)+sin(175)sin(55)

• sin(120)
• cos(120)
• cos(230)
• sin(230)

solve
cos(π/3)cos(2π/3)-sin(π/3)cos(2π/3)

• 1
• -1
• 1/2
• -1/2

Please choose the correct sum and difference formula:
sin (α-β) =

• sin α cos β + cos α sin β
• sin α cos β - cos α sin β
• cos α cos β - sin α sin β
• cos α cos β + sin α sin β

Please choose the correct sum and difference formula:
cos (α+β) =

• sin α cos β + cos α sin β
• sin α cos β - cos α sin β
• cos α cos β - sin α sin β
• cos α cos β + sin α sin β

Please choose the correct sum and difference formula:
cos (α-β) =

• sin α cos β + cos α sin β
• sin α cos β - cos α sin β
• cos α cos β - sin α sin β
• cos α cos β + sin α sin β

Please choose the correct sum and difference formula:
tan (α+β) =

• (tan α + tan β) / (1 - tan α tan β)
• (tan α + tan β) / (1 + tan α tan β)
• (1 - tan α tan β) / (tan α + tan β)
• (1 - tan α tan β) / (tan α + tan β)

Please choose the correct sum and difference formula:
sin (α+β) =

• sin α cos β + cos α sin β
• sin α cos β - cos α sin β
• cos α cos β - sin α sin β
• cos α cos β + sin α sin β

Please choose the correct sum and difference formula:
tan (α-β) =

• (tan α + tan β) / (1 - tan α tan β)
• (tan α - tan β) / (1 + tan α tan β)
• (1 - tan α tan β) / (tan α + tan β)
• (1 - tan α tan β) / (tan α + tan β)

Given sin α = -3/5, cos α = -4/5 and cos β = (2√5)/5, sin β = (-√5)/5
Please find the sum or difference:
cos (α+β)=

• (-11√5)/25
• (-2√5)/25
• (√2-√6)/4
• 2

Find the exact value. 
cos (265 - 25) = 

• 53/12
• -√(3)/2
• -1/2
• √(3)/2