Express equation in another form

Multiply both sides by sinx

3tanx*sinx = 8

 

tanx = sinx/cosx so the above can be written as

3*sin²x/cosx = 8

 

Multiply both sides by cos x

3*sin²x = 8cosx

 

sin²x = 1 - cos²x so the above becomes

3*(1 - cos²x) = 8cosx

3 - 3cos²x = 8cosx

 

Add 3cos²x to both sides of the equation

3 = 3cos²x + 8cosx

 

Subtract 3 from both sides of the equation

0 = 3cos²x + 8cosx - 3

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