Qudratic + Trig (1 Viewer)

[mtsmahia]

Hi Guys,

Can someone please help with this Q .


Solve 3-2cos^2 x - 3sinx=0 for 0* less than or equal to x less than =to 360*

thanks!

 

[Drongoski]

Hi Guys,

Can someone please help with this Q .


Solve 3-2cos^2 x - 3sinx=0 for 0* less than or equal to x less than =to 360*

thanks!

3 - 2cos^2 x - 3sinx = 0

.: 3 - 2(1-sin^2 x) - 3sinx = 0

.: 2sin^2 x - 3sin x + 1 = 0 (a quadratic eqn in sinx like: 2m^2 -3m + 1 = 0)

i.e. (2sinx - 1)(sinx - 1) = 0

.: either 2sinx - 1 = 0 ==> sinx = 1/2 ==> x = 30 deg, 150 deg

or: sinx - 1 = 0 ==> x = 90 deg

 

[mtsmahia]

3 - 2cos^2 x - 3sinx = 0

.: 3 - 2(1-sin^2 x) - 3sinx = 0

.: 2sin^2 x - 3sin x + 1 = 0 (a quadratic eqn in sinx like: 2m^2 -3m + 1 = 0)

i.e. (2sinx - 1)(sinx - 1) = 0

.: either 2sinx - 1 = 0 ==> sinx = 1/2 ==> x = 30 deg, 150 deg

or: sinx - 1 = 0 ==> x = 90 deg

EDIT: sorry, was looking at wrong answer... thanks for the help