Monday, July 29, 2013

Solve the equation cos^2x=1-sinxcosx

We'll move the product sin x*cos x to the left side and
we'll shift (cos x)^2 to the right side:


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


The pythagorean identity
yields:


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


The equation will
become:


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


We'll subtract (sin x)^2 both
sides:


sin x*cos x - (sin x)^2 =
0


We'll factorize by sin
x:


sin x*(cos x - sin x) 
=0


We'll cancel each
factor:


sin x = 0 => x = (-1)^k*arcsin 0 +
2k*pi


x = 0 + 2k*pi


cos x -
sin x = 0


We'll divide by cos
x:


1 - tan x = 0


tan x = 1
=> x = arctan 1 + k*pi


x = pi/4 +
k*pi


The sets of solutions of the equation
are: {0 + 2k*pi}U{pi/4 + k*pi}.

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