Friday, July 6, 2012

If sinx + 3^1/2*cosx = 1 . What is x ?

This is linear equation and we'll solve it using the
helping angle method.


sinx + sqrt3*cosx =
1


We notice that the coefficients of cos x, namely sqrt 3,
could be written as tan pi/3.


We'll substitute sqrt 3 by
tan pi/3 and we'll get:


sinx + tan pi/3*cosx =
1


We'll write tan pi/3 = sin pi/3/cos
pi/3


We'll substitute tan pi/3 by the ratio sin pi/3/cos
pi/3.


sinx + (sin pi/3/cos pi/3)*cosx =
1


We'll multiply by cos pi/3 the terms without
denominator:


sin x*cos pi/3 + sin pi/3*cosx = cos
pi/3


The sum from the left side is the result of applying
the formula;


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


We'll put a = x and b =
pi/3


sin x*cos pi/3 + sin pi/3*cosx = sin (x +
pi/3)


We'll substitute the sum by the sine
function:


sin (x + pi/3) = cos
pi/3


sin (x + pi/3) = 1/2


x +
pi/3 = (-1)^k*arcsin (1/2) + k*pi


x + pi/3 =
pi/6


x = pi/3 - pi/6


x = (2pi
- pi)/6


x =
pi/6


The solution of the
equation is x = pi/6.

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