Θ lies in quadrant III, φ lies in quadrant I. cos θ = -8 /17 , cos φ = 15 /17 . What is cos (θ - φ)?

cos(θ - φ) is -240/289

Step-by-step explanation:

The given parameters are;

The location of θ = Quadrant III

The location of φ = Quadrant I

cos(θ) = -8/17

cos(φ) = 15/17

By trigonometric identities, we have;

cos(θ - φ) = cos(θ)·cos(φ) - sin(θ)·sin(φ)

Given that 'θ' is in quadrant III, we have;

sin(θ) is negative

By Pythagoras' theorem, we have;

∴ sin(θ) = -√(17²- 8²)/17 = -15/17

Whereby 'φ' is in quadrant I, by Pythagoras' theorem, we have;

sin(φ) = √(17² - 15²)/17 = 8/17

∴ cos(θ - φ) = (-8/17) × (15/17) + (-15/17) × (8/17) = -240/289 = -0.83044982699

answer:   28.56 feet (approx)

step-by-step explanation:

since, triangle abc has measure of angle c equal to 55 degrees, measure of angle abc equal to 90 degrees, and length of bc equal to 20 feet.

we have to find out the measurement of segment ab.

therefore, tan 55° =

but bc = 20 feet.

⇒ tan 55 ° =  

⇒ ab = 20 × tan 55 °

⇒ ab = 20 × 1.42814800674

⇒ ab = 28.5629601348   ≈ 28.56 feet

x = 12

y = 1

for the points!