Saturday, August 17, 2013

Solve the system x-y=pi/3 sinx+siny=3^1/2

To solve the system means to find the pair of values for x
and y that verifies the equations of the system.


We'll
re-write the second equation of the system, transforming the sum of like trigonometric
functions into a product:


sin a + sin b = 2sin
[(a+b)/2]*cos [(a-b)/2]


sinx + siny = 2sin [(x+y)/2]*cos
[(x-y)/2]


We'll substitute x - y by pi/3 and we'll
get:


sinx + siny = 2sin [(x+y)/2]*cos
[(pi/3)/2](1)


But sinx + siny = sqrt 3
(2)


We'll put (1) = (2):


2sin
[(x+y)/2]*cos [(pi/3)/2] = sqrt 3


We'll divide by
2:


sin [(x+y)/2]*cos [(pi/6)] = (sqrt
3)/2


We'll substitute cos [(pi/6)] =
sqrt3/2


(sqrt3/2)*sin [(x+y)/2] =
sqrt3/2


We'll divide by
sqrt3/2:


sin [(x+y)/2] =
1


(x+y)/2 = arcsin 1


(x+y)/2 =
pi/2


x + y = 2pi/2


x + y = pi
(3)


x - y = pi/3 (4)


We'll add
(3) + (4):


x + y + x - y = pi +
pi/3


We'll combine and eliminate like
terms:


2x = 4pi/3


We'll divide
by 2:


x =
4pi/6


x =
2pi/3


We'll substitute x in
(3):


2pi/3 + y = pi


We'll
subtract 2pi/3 both sides:


y = pi -
2pi/3 


y =
pi/3


The solution of the
system is represented by the pair (2pi/3 ; pi/3).

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