What is the general solution for cos(x)=-2/5 ?

The general solution for cos(x)=-2/5 is x=1.98231…+2pin,x=-1.98231…+2pin

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cos(x)=-2/5

cos (x) = - \frac{2}{5}

x = 1.98231 \dots + 2 πn, x = - 1.98231 \dots + 2 πn

Solution steps

cos (x) = - \frac{2}{5}

Apply trig inverse properties

x = arccos (- \frac{2}{5}) + 2 πn, x = - arccos (- \frac{2}{5}) + 2 πn

Show solutions in decimal form

x = 1.98231 \dots + 2 πn, x = - 1.98231 \dots + 2 πn

cot^{2} (θ) - 9 = 0

sec (x) = - 1 - tan (x)

sec (θ) + 3 = 0

2 sin (x) cos (x) + 3 sin (x) = 0

cos (2 x) - cos (x) = 0, 0 \leq x < 2 π

What is the general solution for cos(x)=-2/5 ?
The general solution for cos(x)=-2/5 is x=1.98231…+2pin,x=-1.98231…+2pin