What is the general solution for cos(2x)=-0.8 ?

The general solution for cos(2x)=-0.8 is x=(2.49809…)/2+pin,x=-(2.49809…)/2+pin

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cos(2x)=-0.8

cos (2 x) = - 0.8

x = \frac{2.49809 \dots}{2} + πn, x = - \frac{2.49809 \dots}{2} + πn

Solution steps

cos (2 x) = - 0.8

Apply trig inverse properties

2 x = arccos (- 0.8) + 2 πn, 2 x = - arccos (- 0.8) + 2 πn

Solve

2 x = arccos (- 0.8) + 2 πn : x = \frac{arccos ( - 0.8 )}{2} + πn

Solve

2 x = - arccos (- 0.8) + 2 πn : x = - \frac{arccos ( - 0.8 )}{2} + πn

x = \frac{arccos ( - 0.8 )}{2} + πn, x = - \frac{arccos ( - 0.8 )}{2} + πn

Show solutions in decimal form

x = \frac{2.49809 \dots}{2} + πn, x = - \frac{2.49809 \dots}{2} + πn

0 = - 4 sin (2 x)

cot (x) + 1 = 0, 0 \leq x < 2 π

x, cos (k x) = - 1

sec^{2} (x) = \frac{3}{4}

sin (x) = \frac{4.4 sin ( 11 9 ^{\circ} )}{12.3}

What is the general solution for cos(2x)=-0.8 ?
The general solution for cos(2x)=-0.8 is x=(2.49809…)/2+pin,x=-(2.49809…)/2+pin