Sunday

November 23, 2014

November 23, 2014

Posted by **lauren** on Wednesday, January 19, 2011 at 6:40pm.

given sec x = 4, tan x < 0, find sin(2x), cos(2x)and tan (2x)

- trig -
**Reiny**, Wednesday, January 19, 2011 at 7:11pmwe can see that secx > 0 and tanx < 0,

so x must be in quadrants IV

draw a right-angled triangle in that quadrant where

x = 1, y = -4, and r = √17

sinx = -4/√17

cosx = 1/√17

tanx = -4/1 = -4

you should know that:

sin(2x) = 2sinxcos = 2((-4/√17)(1/√17) = -8/17

cos(2x) = cos^2x - sin^2x = 1/17 - 16/17 = -15/17

tan(2x) = sin(2x)/cos(2x) = (-8/17)/(-15/17) = 8/15

**Answer this Question**

**Related Questions**

Integration - Intergrate ¡ì sec^3(x) dx could anybody please check this answer. ...

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

trig 26 - simplify to a constant or trig func. 1. sec ²u-tan ²u/cos ²v+sin ²v ...

Trigonometry desperate help, clueless girl here - 2. solve cos 2x-3sin x cos 2x...

Trigonometry - 1.Solve tan^2x + tan x – 1 = 0 for the principal value(s) to two ...

precalculus - For each of the following determine whether or not it is an ...

more trig.... how fun!!!! - if you can't help me with my first question hopw you...

trigonometry hlp me - 6.Prove that tan y cos^2 y + sin^2y/sin y = cos y + sin y...

Maths Calculus Derivatives - Find the first derivative for the following ...

trig help much appreciated! :)) - 1. Find the complete exact solution of sin x...