Wednesday, October 1, 2014

How can I solve this problem if x is in the real number system and the equation is: sin(x+pi/6)+cos(pi/3-x)=1

sin(x+pi/6) + cos(pi/3) -x) =
1


First we will use trigonometric identities to
solve.


We know that:


sin(a+b)
= sina*cosb + cosa*sinb


==> sin(x+pi/6)=
sinx*cos(pi/6) + cosx*sin(pi/6)


==> sin(x+pi/6)=
(sqrt3 /2 )*sinx + (1/2)*cosx......(1)


cos(a-b)= cosa*cosb
+ sina*sinb


==> cos(pi/3 -x)= cospi/3*cosx +
sinpi/3*sinx


==> cos(pi/3 -x) = (1/2) cosx + sqrt3
/2 * sinx............(2)


Now we will add (1) and
(2):


==> 2(sqr3/2)sinx + 2(1/2)cosx =
1


==> sqr3*sinx + cosx =
1


==> sqrt3 sinx = 1-
cosx


Square both
sides:


==> 3sin^2 x = 1 - 2cosx + cos^2
x


==> 3(1-cos^2 x) = 1- 2cosx + cos^2
x


==> 3 - 3cos^2 x = 1- 2cosx + cos^2
x


==> 4cos^2 x - 2cosx -2 =
0


==> 2cos^2 x - cosx -1 =
0


==> (cosx -1) (2cosx +1) =
0


==> cosx = 1 ==> x = 0, pi,
2pi


==> 2cosx +1 = 0 ==> cosx = -1/2
==> x = 4pi/3 , 5pi/3


==> x = {
0, pi, 4pi/3, 5pi/3, 2pi }

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