# Maths - trig

posted by .

Solve 3cos2x - 7cosx = 0, when 0<=x<=360

And also, find the exact values for x when 0<=x<=360 if 3tan^2x=1

Thankyou!

• Maths - trig -

have you come across
cos 2x = 2cos^2 x - 1 ?
let's sub it.
3cos 2x - 7cosx = 0
3(2cos^2 x - 1) - 7cosx = 0
6cos^2x - 7cosx - 3 = 0
(2cosx-3)(3cosx+1) = 0

cosx = 3/2 , which is not possible,
or
cosx = -1/3
so x must be in quadrants II or III
angle in standard position is 7.53 , then
x = 180-70.53 = 109.47°
or
x = 180+70.53 = 250.53

• 2nd part Maths - trig -

3tan^2 = 1
tan^2x = 1/3
tanx = ± 1/√3

x = 30°, 150°, 210° or 330°

• ìàòåìàòèêà -

3cos2x+7cosx+3=0

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