Cos(2x) = cos^2(x) - sin^2(x) - cos(x)
but sin^2(x) = 1 - cos^2(x)
cos(2x) - cos(x) = cos^2(x) - (1 - cos^2(x) ) - cos(x)
cos(2x) - cos(x) = cos^2(x) - 1 + cos^2(x) - cos(x)
cos(2x) - cos(x) = 2cos^2(x) - 1 - cos(x)
cos(2x) - cos(x) = (2cos(x) + 1)(cos(x) - 1)
I think this is what you have asked for.
You can see 84.78 as 
.
So, you can see the problem as 
First, multiply all the numerators together and all the denominators together.
You end up with 
=33.912
Answer:
18kg is the correct answer
Answer:
A ≈ 9.0 ft²
Step-by-step explanation:
70° = 7π/18 radians
Area of the arc section
A = ½(7π/18)8² = 12⁴/₉π ft² = 39.09537 ft²
As the triangle is isosceles, the other two angles are (180 - 70) / 2 = 55°
law of sines 8 / sin55 = L / sin 70 L = 9.17722
so the triangle height = √(8² - (9.17722/2)²) = 6.55321
Area of triangle ½(6.55321)(9.17722) = 30.07016
Area = 39.09537 - 30.07016 = 9.025211 ≈ 9.0 ft²
