How to solve the trig equation: #sqrt(1+cos(x))-sqrt(1-sin(x))=1#?

1 Answer
Jun 4, 2017

Given: #sqrt(1+cos(x))-sqrt(1-sin(x))=1#

Square both sides:

#1 + cos(x) -2sqrt(1+cos(x))sqrt(1-sin(x)) + 1 - sin(x) = 1#

#cos(x) -sin(x) + 1 = 2sqrt(1+cos(x))sqrt(1-sin(x))#

Square both sides:

#cos^2(x) - sin(x)cos(x)+cos(x)-sin(x)cos(x)+sin^2(x)-sin(x)+cos(x)-sin(x)+1 = 4(1+cos(x))(1-sin(x))#

# 2cos(x)- 2sin(x)cos(x)-2sin(x)+2 = 4(1+cos(x))(1-sin(x))#

# cos(x)- sin(x)cos(x)-sin(x)+1 = 2(1+cos(x)-sin(x) - sin(x)cos(x))#

# cos(x)- sin(x)cos(x)-sin(x)+1 = 2+2cos(x)-2sin(x) - 2sin(x)cos(x)#

# cos(x)- sin(x)cos(x)-sin(x)+1 = 0#

Factor:

#(1 + cos(x))(1 - sin(x)) = 0#

#cos(x) = -1 and sin(x) = 1#

check #cos(x) = -1# then #sin(x) = 0#:

#sqrt(1-1)-sqrt(1-0)=1#

#-1 = 1#

This does not check; discard the root #cos(x) = -1#

check #sin(x) = 1#, then #cos(x) = 0#:

#sqrt(1-0)-sqrt(1-1)=1#

#1 = 1#

This checks

Find repetitive values of x where #sin(x) =1#

#x = sin^-1(1)#

#x = pi/2#

This repeats at integer multiples of #2pi#:

#x = pi/2 + 2pin; n in ZZ#