What is the general solution for cos(2a)=-4/7 ?

The general solution for cos(2a)=-4/7 is a=(2.17904…)/2+pin,a=-(2.17904…)/2+pin

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cos(2a)=-4/7

cos (2 a) = - \frac{4}{7}

a = \frac{2.17904 \dots}{2} + πn, a = - \frac{2.17904 \dots}{2} + πn

Solution steps

cos (2 a) = - \frac{4}{7}

Apply trig inverse properties

2 a = arccos (- \frac{4}{7}) + 2 πn, 2 a = - arccos (- \frac{4}{7}) + 2 πn

Solve

2 a = arccos (- \frac{4}{7}) + 2 πn : a = \frac{arccos ( - \frac{4}{7} )}{2} + πn

Solve

2 a = - arccos (- \frac{4}{7}) + 2 πn : a = - \frac{arccos ( - \frac{4}{7} )}{2} + πn

a = \frac{arccos ( - \frac{4}{7} )}{2} + πn, a = - \frac{arccos ( - \frac{4}{7} )}{2} + πn

Show solutions in decimal form

a = \frac{2.17904 \dots}{2} + πn, a = - \frac{2.17904 \dots}{2} + πn

cos (\frac{π}{60}) - cos (\frac{π}{60}) = sin (x)

3 tan^{2} (α) - 3 tan (α) = 0

cos (θ) = - \frac{12}{13}

- tan (x) = 0

3 sin (θ) + 1 = 1

What is the general solution for cos(2a)=-4/7 ?
The general solution for cos(2a)=-4/7 is a=(2.17904…)/2+pin,a=-(2.17904…)/2+pin