Asked by elise
Solve the multiple-angle equation.
cos x/2 = - squareroot 3/2
cos x/2 = - squareroot 3/2
Answers
Answered by
elise
sorry that is supposed to be math not amth!
Answered by
Reiny
I know cos 30° or cos π/6 = +√3/2
so x/2 = 180-30 or x/2 = 180+30
x = 300° or x = 420°
or
x = 5π/3 or 7π/3
To do these type of questions, you MUST know the ratio of sides of the 30-60-90° as well as the 45-45-90° triangles, and you MUST be able to recognize the trig ratios.
e.g. I immediately saw that √3/2 came from the 30-60-90 triangle.
so x/2 = 180-30 or x/2 = 180+30
x = 300° or x = 420°
or
x = 5π/3 or 7π/3
To do these type of questions, you MUST know the ratio of sides of the 30-60-90° as well as the 45-45-90° triangles, and you MUST be able to recognize the trig ratios.
e.g. I immediately saw that √3/2 came from the 30-60-90 triangle.
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