Posted by **Carry** on Monday, February 23, 2009 at 8:45pm.

tan(X+30)tan(30-x)=2cos2x-1 / (2cos2x+1)

i just did

(tanx)(-tanx)=-sin^2x/cos^2x would taht work?

- Trig check my work please? -
**Reiny**, Monday, February 23, 2009 at 9:44pm
no, just test it for some value of x

LS is not equal to your RS

- Trig check my work please? -
**Reiny**, Monday, February 23, 2009 at 10:19pm
Carry, where are you getting these,

even though I enjoy doing them, they are getting to me, lol

recall tan(A+B) = (tanA + tanB)/(1 - tanAtanB)

so LS

= (tanx + tan30)/1-tanxtan30)*(tan30-tanx)/(1+tanxtan30)

= (tan^2 30 - tan^2 x)/(1 - (tan^x)(tan^2 30))

now tan^2 30º = 1/3

so the above

= (1/3 - tan^2 x)/(1 - (1/3)tan^2 x)

multiply top and bottom by 3 to get

(1 - 3tan^2 x)/(3 - tan^2 x)

RS = (2cos(2x) - 1)/(2cos(2x) + 1)

= (2(cos^2x - sin^2x) - 1)/(2(cos^2x-sin^2x) + 1)

remember 1 = sin^2x + cos^2x , so we get

(2cos^2x - 2sin^x - sin^2x - cos^2x)/(2cos^2x - 2sin^2x + sin^2x + cos^2x)

= (cos^2x - 3sin^2x)/(3cos^2x - sin^2x)

divide top and bottom by cos^x to get

(1 - 3tan^2x)/(3 - tan^2x)

ok, no more!!!!

## Answer this Question

## Related Questions

- trigonometry (please double check this) - Solve the following trig equations. ...
- Pre-Calc - How do I solve this? My work has led me to a dead end. tan(45-x) + ...
- Trig - Verify that each of the following is an identity. tan^2x-sin^2x=tan^2xsin...
- Math - How do I solve this? tan^2x= 2tanxsinx My work so far: tan^2x - 2tanxsinx...
- trig - We are doing trig identities in school. I need help with these five: 1.1+...
- Trigonometry - Given that a^2+b^2=2 and that (a/b)= tan(45degee+x), find a and b...
- Trigo - Given that a^2+b^2=2 and that (a/b)= tan(45degee+x), find a and b in ...
- Trig. - sec^2xcotx-cotx=tanx (1/cos)^2 times (1/tan)-(1/tan)=tan (1/cos^2) times...
- solving trig. equations - tan(3x) + 1 = sec(3x) Thanks, pretend 3x equals x so ...
- trig - it says to verify the following identity, working only on one side: cotx+...