Yahoo Answers is shutting down on May 4th, 2021 (Eastern Time) and the Yahoo Answers website is now in read-only mode. There will be no changes to other Yahoo properties or services, or your Yahoo account. You can find more information about the Yahoo Answers shutdown and how to download your data on this help page.

Trig Identity: Can you prove that tan(x) = sin(2x)/[1+cos(2x)]. Thanks?

6 Answers

Relevance
  • gilvi
    Lv 7
    1 decade ago
    Favorite Answer

    tan(x) = sin(2x)/[1+cos(2x)]

    sin(2x) = 2sinxcosx;

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

    tan(x) = 2sinxcosx/[1+cos^2(x) -sin^2(x)]

    tan(x) = 2sinxcosx/[1+cos^2(x) -1 +cos^2(x)] <= sin^2(x) = 1 - cos^2(x)

    tan(x) = 2sinxcosx/[2cos^2(x)]

    tan(x) = sinx/[cos(x)]

    tan(x) = tan(x);

  • Anonymous
    5 years ago

    RHS = (tan pi/4 - tan x)/(a million+ tan x tan pi/4) = (a million-tan x)/(a million+an x) = (cos x -sin x)/(sin x+ cos x) = ( cos x- sin x)(sin x + cos x)/(sin x+ cos x)^2 = (cos ^2 x -sin ^2 x)/(sin ^2 x+ cos^2 x + 2 sin x cos x) = cos 2x/(a million+ sin 2x)

  • ?
    Lv 4
    1 decade ago

    tan (x) = sin (2x)/[1+cos (2x)]

    forms of equation that may derived:

    sin (2x) = 2sin x cos x

    cos (2x) = 2cos² x - 1

    tan x = [2sin x cos x] / [1+2cos² x -1]

    tan x = [2sin x cos x] / [1-1+2cos² x]

    tan x = [2sin x cos x] / [2cos² x] ..... cancel the 2 of

    numerator and denominator gives you...

    tan x = [sin x cos x] / [cos² x] ......... divide the numerator and denominator.

    tan x = sin x/cos x

    tan x = tan x

  • 1 decade ago

    RHS=2sinxcosx/(1+2cos^2x-1)

    =2sinxcosx/2cos^2x

    =sinx/cosx=tanx=LHS

  • 1 decade ago

    x = 6

  • cidyah
    Lv 7
    1 decade ago

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

    using sin(2x)=2 sin(x) cos(x)

    and cos(2x)=1-2sin^2(x)

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

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

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

    =tan(x)

Still have questions? Get your answers by asking now.