a. The value of cos2θ = -119/169
b. The value of cosθ = -5/13
The question involves trigonometric identities
Trigonometric identities show the relationship between trigonometric ratios.
Since sinθ = 12/13 and θ is the quadrant II, it means that 90° ≤ θ ≤180° and sinθ is positive.
Using trigonometric identity
cos2θ = 1 - 2sin²θ
Substituting sinθ = 12/13 into the equation, we have
cos2θ = 1 - 2sin²θ
cos2θ = 1 - 2(12/13)²
cos2θ = 1 - 2(144/169)
cos2θ = 1 - 288/169
cos2θ = (169 - 288)/169
cos2θ = -119/169
So, the value of cos2θ = -119/169
Since sinθ = 12/13 and θ is the quadrant II, it means that 90° ≤ θ ≤180° and sinθ is positive.
Using trigonometric identity
cosθ = √(1 - sin²θ)
Substituting sinθ = 12/13 into the equation, we have
cosθ = √(1 - sin²θ)
cosθ = √[1 - (12/13)²]
cosθ = √[1 - (144/169)]
cosθ = ±√(169 - 144)/169
cosθ = ±√25/169
cosθ = ±5/13
θ is the quadrant II, it means that 90° ≤ θ ≤180° it means that cosθ is negative.
So, cosθ = -5/13
So, the value of cosθ = -5/13
Learn more about trigonometric identities here:
https://brainly.com/question/27990864
#SPJ1
