Posted by **Edward** on Wednesday, April 11, 2007 at 2:25pm.

Solve this equation fo rx in the interval 0<=x<=360

3sinxtanx=8

I would do it this way:

sinxtanx = 8/3

sinx(sinx/cosx)=8/3

sin^2x/cosx = 8/3

(1-cos^2x)/cosx=8/3

cross-multiply

3 - 3cos^2x = 8cosx

3cos^2x + 8cosx - 3 = 0

(3cosx-1)(cosx+3)=0

cosx=1/3 or cosx = -3

the last one is not possible

so x = arccos(1/3)=70.5º

or 289.5º (in the fourth quadrant)

## Answer this Question

## Related Questions

- Trig - prove the identity (sinX)^6 +(cosX)^6= 1 - 3(sinX)^2 (cosX)^2 sinX^6= ...
- maths - by equating the coefficients of sin x and cos x , or otherwise, find ...
- Trig........ - I need to prove that the following is true. Thanks (cosx / 1-sinx...
- Trigonometry. - ( tanx/1-cotx )+ (cotx/1-tanx)= (1+secxcscx) Good one! ...
- Pre-Calc - Trigonometric Identities Prove: (tanx + secx -1)/(tanx - secx + 1)= ...
- Trigonometry Check - Simplify #3: [cosx-sin(90-x)sinx]/[cosx-cos(180-x)tanx] = [...
- Precalculus/Trig - I can't seem to prove these trig identities and would really ...
- maths - trigonometry - I've asked about this same question before, and someone ...
- Math - Pre- Clac - Prove that each of these equations is an identity. A) (1 + ...
- Calculus 2 Trigonometric Substitution - I'm working this problem: ∫ [1-tan...

More Related Questions