Tuesday, October 26, 2010

What is the solution of equation sin^2x+sinx*cosx=1?

We'll shift (sin x)^2 to the right
side:


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


But, from Pythagorean identity, we'll
have:


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


The equation will
become:


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


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


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


We'll factorize by cos
x:


cos x*(sin x - cos x) 
=0


We'll cancel each
factor:


cos x = 0 => x = +/-arccos 0 +
2k*pi


x = +/-(pi/2)
+ 2k*pi


sin x - cos x =
0


We'll divide by cos x:


tan x
- 1 = 0


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


x = pi/4 +
k*pi


The solutions of the equation belong to
the reunion of the following sets: {+/-(pi/2) + 2k*pi}U{pi/4 +
k*pi}.

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