trignometry
posted by help me out it's urgent .
show that cos2x=1tan^ 2 x /1+tan^2x=2cos^2x1

cos 2x
= cos(x+x)
= cosxcosx  sinxsinx
= cos^2 x  sin^2 x
= cos^2 x  (1  cos^2 x)
= 2 cos^2 x  1, the last part of your equation.
all we need it to look at now is the middle part of
(1  tan^2 x)/(1 + tan^2 x) , notice the necessary brackets
= (1  sin^2 x/cos^2 x)/(1 + sin^2 x/cos^2 x)
= [ (cos^2 x  sin^2 x)/cos^2 x ]/[ (cos^2 x + sin^2 x)/cos^2 x ]
= (cos^2 x  sin^2 x)/cos^2 x * cos^2 x/(cos^2 x + sin^2 x)
= (cos^2 x  sin^2 x)/1
= cos^2 x  sin^2 x
as seen above
Respond to this Question
Similar Questions

Trig.......
I need to prove that the following is true. Thanks (2tanx /1tan^x)+(1/2cos^2x1)= (cosx+sinx)/(cosx  sinx) and thanks ........... check your typing. I tried 30ยบ, the two sides are not equal, they differ by 1 oh , thank you Mr Reiny … 
verifying identities
how do you veriy tan x + Cot y  = tan y + cot x 1tan x cot y sin^4x + cos^4x = 1 2cos^2x + 2cos^4 
Trig.
sec^2xcotxcotx=tanx (1/cos)^2 times (1/tan)(1/tan)=tan (1/cos^2) times (2/tan)=tan (2/cos^2tan)times tan=tan(tan) sq. root of (2/cos^2)= sq. root of (tan^2) sq. root of (2i)/cos=tan I'm not sure if I did this right. If I didn't, … 
Trigonometry
Find the exact value of tan(ab) sin a = 4/5, 3pi/2<a<pi; tan b = sqrt2, pi/2<b<pi identity used is: tan(ab)=(tan atan b)/1+tan a tan b simplify answer using radicals. (a is alpha, b is beta) 
math
if sin(x+α)=2cos(xb) show tan x such that : tan x=(2tan α)/(12 tan α) 
mathstrignometry
Prove that tan1 (1/7) + tan1 (1/13) = tan1(2/9) 
MathTrigonometry
Show that if A, B, and C are the angles of an acute triangle, then tan A + tan B + tan C = tan A tan B tan C. I tried drawing perpendiculars and stuff but it doesn't seem to work? 
trignometry
Tan4x=4tanx(1tan^x)/16tan^x+tan^^x ,prove 
Math
prove sin2x+cos2x+1 tan(pi/4+x) ______________ = __________ sin2x+cos2x1 tanx so what I did tan(x) (1+cos(2x)+sin(2x)=tan(pi/4+x) (1+cos(2x)+sin(2x) 
basic maths trignometry
prove that secx  tanx = 1 tan x/2 /1 + tan x/2