Friday

July 25, 2014

July 25, 2014

Posted by **Hayden** on Wednesday, February 18, 2009 at 4:54pm.

if tan x=2 cosx>0

- trig -
**Damon**, Wednesday, February 18, 2009 at 5:17pmfirst quadrant because sin and cos are +

triangle is 1, 2, sqrt 45

sin x = 2/sqrt 5

cos x = 1/sqrt 5

I think you can take it from there

- trig -
**Reiny**, Wednesday, February 18, 2009 at 5:22pmsince both the cosine and the tangent are positive, x must be an angle in the first quadrant.

from tanx = 2/1, draw a right-angled triangle with angle x at the origin that has a height of 2, and a base of 1

(tangentx = opposite/adjacent, so the opposite is 2 and the adjacent is 1)

so by Pythagoras, the hypotenuse is √5

so sinx - 2/√5 and cosx = 1/√5

sin2x = 2sinxcosx (one of our general identities)

= 2(2/√5)(1/√5) = 4/5

you can check this on the calculator

take inverse tan of 2 to get the angle,

double that angle

take the sine

you should get .8 which is 4/5

**Related Questions**

Trig Identities - Proving identities: 1) 1+ 1/tan^2x = 1/sin^2x 2) 2sin^2 x-1 = ...

Trig....... - I need to prove that the following is true. Thanks (2tanx /1-tan^x...

Trigonometry - Prove the following trigonometric identities. please give a ...

Math-Trig - 1. Create an algebraic expression for sin(arccosx-arcsin3x) 2. The ...

Trig - Given: cos u = 3/5; 0 < u < pi/2 cos v = 5/13; 3pi/2 < v < ...

trig - how do i find cosX if i am given sin x= -4/5 and tan <o???

TRIG.............. - Q.1 Prove the following identities:- (i) tan^3x/1+tan^2x + ...

trig 26 - simplify to a constant or trig func. 1. sec Ču-tan Ču/cos Čv+sin Čv ...

trig - prove the following trig identity: a) sin(pi/6 + x) + sin (pi/3 + x) + ...

Trig........ - I need to prove that the following is true. Thanks (cosx / 1-sinx...