Sum and difference formulas

Find the exact value of the expression.
cos(20)cos(40) - sin(20)sin(40)

• 1/4
• 1/2
• √(3)/2
• √(3)

Tags

CCSS.HSF.TF.C.9

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

• 53/12
• -√(3)/2
• -1/2
• √(3)/2

Tags

CCSS.HSF.TF.C.9

Use Sum or Difference Identities to find the exact value of each expression.
cos(75°)

• 1/4
• ( √(6) - √(2) ) / 4
• (√(6) + √(2)) / 4
• (-√(6) - √(2)) / 4

Tags

CCSS.HSF.TF.C.9

Given  $\sin\alpha=-\frac{3}{5},\ \cos\alpha=-\frac{4}{5}$   and  $\cos\beta=\frac{2\sqrt{5}}{5},\ \sin\beta=-\frac{\sqrt{5}}{5}$   
Find the exact value of sin (α+β):

• 0

•  $-\frac{2\sqrt{5}}{25}$  

•  $\frac{\sqrt{2}-\sqrt{6}}{4}$  

•  $\frac{\sqrt{8}}{4}$  

Tags

CCSS.HSF.TF.C.9

Use a sum or difference formula to find an exact value of sin 105º

• $\frac{\sqrt{3}}{2}$

• $\frac{-\sqrt{2}-\sqrt{6}}{4}$

• $\frac{\sqrt{2}+\sqrt{6}}{4}$

• $2-\sqrt{3}$

Tags

CCSS.HSF.TF.C.9