Double Angle Identity

sin2u =

• (sinu)(cosu)
• 2(sinu)(cosu)
• (sinu)^2
• 2(sinu)^2

cos2u =

• 2(sinu)(cosu)
• (cosu)^2 - (sinu)^2
• 2(cosu)^2 - 2
• (sinu)^2 - (cosu)^2

If cosx = - 4/5, find csc if in quadrant II

• 1/2
• -3/5
• 5/3
• √3/2

If cosx = - 4/5, find secx.

• -5/4

• -3/5

• 5/3

• √3/2

Find the exact value of sin 2x if sin x = 12/13 and x is in the first quadrant. 

• 120/169
• 25/169
• 60/169
• 5/13

Using the second identity, find Cos(50)

• sin²(25) - cos²(25) 
• cos²(50) - sin²(50)
• cos²(25) - sin²(25)
• sin²(50) - cos²(50) 

Using the first identity, find Sin(180)

• 2sin(90)cos(90)
• 2sin(180)cos(180)
• sin(90)cos(90)
• sin(180)cos(180)

Using the third identity, find Cos(40)

• 2cos² (40) - 1
• 2cos² (20) - 1
• 2cos² (20) + 1
• 2cos² (40) + 1

Using the fourth identity, find Cos(120)

• 1-2sin²(120)
• 1+2sin²(120)
• 1+2sin²(60)
• 1-2sin²(60)

Use a double-angle identity to find the exact value of each expression
cos θ = 4/5 and 270° < θ < 360°
Find sin 2θ

• -1/5
• 24/25
• -24/25
• -25/24