Math  Solving Trig Equations
posted by Anonymous .
What am I doing wrong?
Equation:
sin2x = 2cos2x
Answers:
90 and 270
....
My Work:
2sin(x)cos(x) = 2cos(2x)
sin(x) cos(x) = cos(2x)
sin(x) cos(x) = 2cos^2(x)  1
cos(x) (+/)\sqrt{1  cos^2(x)} = 2cos^2(x)  1
cos^2(x)(1  cos^2(x)) = 4cos^4(x)  4cos^2(x) + 1
5cos^4(x)  5cos^2(x) + 1 = 0
cos(x) = (+/) 0.85065080835215
cos(x) = (+/)0.52573111211905

Math  Solving Trig Equations 
bobpursley
wouldn't it be easier to solve for 2x then divide it by two?
sin2x=2cos2x
sin2x/cos2x=2
tan 2x=2
2x=63.43 deg
x= .... you do it.
Respond to this Question
Similar Questions

trig
Reduce the following to the sine or cosine of one angle: (i) sin145*cos75  cos145*sin75 (ii) cos35*cos15  sin35*sin15 Use the formulae: sin(a+b)= sin(a) cos(b) + cos(a)sin(b) and cos(a+b)= cos(a)cos(b)  sin(a)sin)(b) (1)The quantity … 
tigonometry
expres the following as sums and differences of sines or cosines cos8t * sin2t sin(a+b) = sin(a)cos(b) + cos(a)sin(b) replacing by by b and using that cos(b)= cos(b) sin(b)= sin(b) gives: sin(ab) = sin(a)cos(b)  cos(a)sin(b) … 
algebra
Can someone please help me do this problem? 
Mathematics  Trigonometric Identities
Let y represent theta Prove: 1 + 1/tan^2y = 1/sin^2y My Answer: LS: = 1 + 1/tan^2y = (sin^2y + cos^2y) + 1 /(sin^2y/cos^2y) = (sin^2y + cos^2y) + 1 x (cos^2y/sin^2y) = (sin^2y + cos^2y) + (sin^2y + cos^2y) (cos^2y/sin^2y) = (sin^2y … 
Math  Solving for Trig Equations
Solve the following equation for 0 less than and/or equal to "x" less than and/or equal to 360  cos^2x  1 = sin^2x  Attempt: cos^2x  1  sin^2x = 0 cos^2x  1  (1  cos^2x) = 0 cos^2x  1  1 + cos^2x = 0 2cos^2x  2 = 0 (2cos^2x/2)= … 
Math  Solving Trig Equations
Solve each equation for o is less than and/or equal to theta is less than and/or equal to 360  sin^2x = 1 = cos^2x  Work: cos^2x  cos^2x = 0 0 = 0  Textbook Answers: 90 and 270  Btw, how would you isolate for cos^2x = 0? 
TRIG!
Posted by hayden on Monday, February 23, 2009 at 4:05pm. sin^6 x + cos^6 x=1  (3/4)sin^2 2x work on one side only! Responses Trig please help!  Reiny, Monday, February 23, 2009 at 4:27pm LS looks like the sum of cubes sin^6 x + cos^6 … 
Precal
I do not understand how to do this problem ((sin^3 A + cos^3 A)/(sin A + cos A) ) = 1  sin A cos A note that all the trig terms are closed right after there A's example sin A cos A = sin (A) cos (A) I wrote it out like this 0 =  … 
trigonometry (please double check this)
Solve the following trig equations. give all the positive values of the angle between 0 degrees and 360 degrees that will satisfy each. give any approximate value to the nearest minute only. 1. sin2ƒÆ = (sqrt 3)/2 2. sin^2ƒÆ = … 
trig
I don't understand this. can you please tell how you got each answer?