How do you solve (cot x)+ sqrt(3) = (csc x)(cotx)+3=(cscx)?

2 Answers
Apr 6, 2018

color(blue)(x=(2pi)/3+2npi)x=2π3+2nπ

Explanation:

Identities:

color(red)bb(cotx=cosx/sinx)cotx=cosxsinx

color(red)bb(cscx=1/sinx)cscx=1sinx

Substituting these into given equation:

cosx/sinx+sqrt(3)=1/sinxcosxsinx+3=1sinx

cosx/sinx+sqrt(3)-1/sinx=0cosxsinx+31sinx=0

Add LHS:

(cosx+sqrt(3)sinx-1)/sinx=0cosx+3sinx1sinx=0

This can only be true if the numerator equals zero. we can't have division by zero.

:.

cosx+sqrt(3)sinx-1=0

cosx-1=-sqrt(3)sinx

Square both sides:

(cosx-1)^2=3sin^2x

Identity:

color(red)bb(sin^2x+cos^2x=1)

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

Expanding:

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

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

Let m=cosx

:.

4m^2-2m-2=0

Factor:

(2m+1)(2m-2)=0=>m=-1/2 and m=1

x=arccos(cosx)=arccos(-1/2)=>color(blue)(x=(2pi)/3+n2pi)

x=arccos(cosx)=arccos(1)=>x=2pin

cscx and cotx are undefined for 2pin (division by zero)

Only:

color(blue)(x=(2pi)/3+2npi)

n in ZZ

Apr 6, 2018

x=2kpi+(2pi)/3,kinZZ
We know that,
color(red)((1) cos(A-B)=cosAcosB+sinAsinB
color(red)((2)costheta=cosalpha=>theta=2kpi+-alpha,kinZZ

Explanation:

Here,

cotx+sqrt3=cscx

=>cosx/sinx+sqrt3=1/sinx

We take , denominator color( blue)(sinx!=0=>x!=kpi,kinZZ.

So,

cosx+sqrt3sinx=1

Dividing both sides by 2

1/2cosx+sqrt3/2sinx=1/2

=>cosxcos(pi/3)+sinxsin(pi/3)=cos(pi/3)...to color(green) (Apply(1)

=>cos(x-pi/3)=cos(pi/3)

=>x-pi/3=2kpi+-pi/3,kinZZ...tocolor(green)( Apply(2)

=>x=2kpi+pi/3+pi/3,kinZZ or x=2kpi+pi/3-pi/3,kinZZ

=>x=2kpi+(2pi)/3,kinZZ or x=2kpi,kinZZ

But , x!=kpi, kinZZ=>x!=2kpi,kinZZ

Hence,

=x=2kpi+(2pi)/3,kinZZ