Question #58bec

2 Answers
Mar 13, 2017

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

Explanation:

"let " sin(pi/3+x)-cos(pi/6+x) " be equal to 'k' "

sin(a+b)=sin a*cos b +cos a * sin b

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

sin(pi/3+x)=sqrt 3/2*cos x+1/2*sin x

cos(a+b)=cos a*cos b-sin a*sin b

cos(pi/6+x)=cos(pi/6)*cos x-sin(pi/6)*sin x

cos(pi/6+x)=sqrt 3/2*cos x-1/2* sin x

sqrt 3/2*cos x+1/2*sin x-(sqrt 3/2*cos x-1/2* sin x)

cancel(sqrt 3/2*cos x)+1/2*sin x-cancel(sqrt 3/2*cos x)+1/2 *sin x=k

1/2*sin x+1/2*sin x=k

1/2 sin x(1+1)=k

1/cancel(2) *cancel(2) sin x=k

sin x=k

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

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

Mar 14, 2017

Refer to the Explanation Section below.

Explanation:

As a Second Method, let us solve this as under :

Let (pi/3+x)=A, and, (pi/6+x)=B rArr A+B=pi/2+2x.

:. A=pi/2+(2x-B).

Hence, the R.H.S. =sinA-cosB,

=sin{pi/2+(2x-B)}-cosB,

=cos(2x-B)-cosB,....[because, sin(pi/2+theta)=costheta].

But, cosC-cosD=-2sin((C+D)/2)sin((C-D)/2).

:."The R.H.S.="-2sin{((2x-B)+B)/2}sin{((2x-B)-B)/2}

=-2sinxsin(x-B)

Here, B=pi/6+x rArr x-B=-pi/6.

:."The R.H.S.="-2sinxsin(-pi/6),

=(-2sinx)(-sin(pi/6)),

=(-2sinx)(-1/2),

=sinx

="The L.H.S."

Enjoy Maths.!