Here is a step by step explanation! But, prepare yourself, it is very lengthy!!:
Verify the following identity:
(1+tan(3 t))/(1-tan(3 t)) = tan(pi/4+3 t)
Multiply both sides by 1-tan(3 t):
1+tan(3 t) = ^?tan(pi/4+3 t) (1-tan(3 t))
Write tangent as sine/cosine:
1+(sin(3 t))/(cos(3 t)) = ^?(1-(sin(3 t))/(cos(3 t))) (sin(pi/4+3 t))/(cos(pi/4+3 t))
(1-((sin(3 t))/(cos(3 t)))) ((sin(pi/4+3 t))/(cos(pi/4+3 t))) = ((1-(sin(3 t))/(cos(3 t))) sin(pi/4+3 t))/(cos(pi/4+3 t)):
1+(sin(3 t))/(cos(3 t)) = ^?(sin(pi/4+3 t) (1-(sin(3 t))/(cos(3 t))))/(cos(pi/4+3 t))
Put 1+(sin(3 t))/(cos(3 t)) over the common denominator cos(3 t): 1+(sin(3 t))/(cos(3 t)) = (cos(3 t)+sin(3 t))/(cos(3 t)):
(cos(3 t)+sin(3 t))/(cos(3 t)) = ^?(sin(pi/4+3 t) (1-(sin(3 t))/(cos(3 t))))/(cos(pi/4+3 t))
Put 1-(sin(3 t))/(cos(3 t)) over the common denominator cos(3 t): 1-(sin(3 t))/(cos(3 t)) = (cos(3 t)-sin(3 t))/(cos(3 t)):
(cos(3 t)+sin(3 t))/(cos(3 t)) = ^?((cos(3 t)-sin(3 t))/(cos(3 t)) sin(pi/4+3 t))/(cos(pi/4+3 t))
Cross multiply:
cos(3 t) cos(pi/4+3 t) (cos(3 t)+sin(3 t)) = ^?cos(3 t) sin(pi/4+3 t) (cos(3 t)-sin(3 t))
Divide both sides by cos(3 t):
cos(pi/4+3 t) (cos(3 t)+sin(3 t)) = ^?sin(pi/4+3 t) (cos(3 t)-sin(3 t))
cos(pi/4+3 t) = cos(pi/4) cos(3 t)-sin(pi/4) sin(3 t):
cos(pi/4) cos(3 t)-sin(pi/4) sin(3 t) (cos(3 t)+sin(3 t)) = ^?sin(pi/4+3 t) (cos(3 t)-sin(3 t))
cos(pi/4) = 1/sqrt(2):
(1/sqrt(2) cos(3 t)-sin(pi/4) sin(3 t)) (cos(3 t)+sin(3 t)) = ^?sin(pi/4+3 t) (cos(3 t)-sin(3 t))
sin(pi/4) = 1/sqrt(2):
((1 cos(3 t))/sqrt(2)-1/sqrt(2) sin(3 t)) (cos(3 t)+sin(3 t)) = ^?sin(pi/4+3 t) (cos(3 t)-sin(3 t))
((1 cos(3 t))/sqrt(2)-(1 sin(3 t))/sqrt(2)) (cos(3 t)+sin(3 t)) = cos(3 t)^2/sqrt(2)-sin(3 t)^2/sqrt(2):
cos(3 t)^2/sqrt(2)-sin(3 t)^2/sqrt(2) = ^?sin(pi/4+3 t) (cos(3 t)-sin(3 t))
cos(3 t)^2 = 1/2 (1+cos(6 t)):
1/sqrt(2) (1+cos(6 t))/2-sin(3 t)^2/sqrt(2) = ^?sin(pi/4+3 t) (cos(3 t)-sin(3 t))
(1+cos(6 t))/2 = 1/2+1/2 cos(6 t):
1/sqrt(2) 1/2+(cos(6 t))/2-sin(3 t)^2/sqrt(2) = ^?sin(pi/4+3 t) (cos(3 t)-sin(3 t))
sin(3 t)^2 = 1/2 (1-cos(6 t)):
(1 (1/2+(cos(6 t))/2))/(sqrt(2))-1/sqrt(2) (1-cos(6 t))/2 = ^?sin(pi/4+3 t) (cos(3 t)-sin(3 t))
(1-cos(6 t))/2 = 1/2-1/2 cos(6 t):
(1 (1/2+(cos(6 t))/2))/(sqrt(2))-1/sqrt(2) 1/2-(cos(6 t))/(2) = ^?sin(pi/4+3 t) (cos(3 t)-sin(3 t))
(1 (1/2+(cos(6 t))/2))/(sqrt(2)) = 1/(2 sqrt(2))+(cos(6 t))/(2 sqrt(2)):
(1)/(2 sqrt(2))+(1)/(2 sqrt(2)) cos(6 t)-(1 (1/2-(cos(6 t))/(2)))/(sqrt(2)) = ^?sin(pi/4+3 t) (cos(3 t)-sin(3 t))
-(1 (1/2-(cos(6 t))/(2)))/(sqrt(2)) = (cos(6 t))/(2 sqrt(2))-1/(2 sqrt(2)):
(1)/(2 sqrt(2))+(1)/(2 sqrt(2)) cos(6 t)+(cos(6 t))/(2 sqrt(2))-(1)/(2 sqrt(2)) = ^?sin(pi/4+3 t) (cos(3 t)-sin(3 t))
(1)/(2 sqrt(2))+cos(6 t) (1)/(2 sqrt(2))-(1)/(2 sqrt(2))+cos(6 t) (1)/(2 sqrt(2)) = (cos(6 t))/sqrt(2):
(cos(6 t))/sqrt(2) = ^?sin(pi/4+3 t) (cos(3 t)-sin(3 t))
sin(pi/4+3 t) = cos(3 t) sin(pi/4)+cos(pi/4) sin(3 t):
(cos(6 t))/sqrt(2) = ^?cos(3 t) sin(pi/4)+cos(pi/4) sin(3 t) (cos(3 t)-sin(3 t))
sin(pi/4) = 1/sqrt(2):
(cos(6 t))/sqrt(2) = ^?(cos(3 t)-sin(3 t)) (1/sqrt(2) cos(3 t)+cos(pi/4) sin(3 t))
cos(pi/4) = 1/sqrt(2):
(cos(6 t))/sqrt(2) = ^?(cos(3 t)-sin(3 t)) ((1 cos(3 t))/sqrt(2)+1/sqrt(2) sin(3 t))
(cos(3 t)-sin(3 t)) ((cos(3 t) 1)/sqrt(2)+(1 sin(3 t))/sqrt(2)) = cos(3 t)^2/sqrt(2)-sin(3 t)^2/sqrt(2):
(cos(6 t))/sqrt(2) = ^?cos(3 t)^2/sqrt(2)-sin(3 t)^2/sqrt(2)
cos(3 t)^2 = 1/2 (1+cos(6 t)):
(cos(6 t))/sqrt(2) = ^?1/sqrt(2) (1+cos(6 t))/2-sin(3 t)^2/sqrt(2)
(1+cos(6 t))/2 = 1/2+1/2 cos(6 t):
(cos(6 t))/sqrt(2) = ^?1/sqrt(2) 1/2+(cos(6 t))/2-sin(3 t)^2/sqrt(2)
sin(3 t)^2 = 1/2 (1-cos(6 t)):
(cos(6 t))/sqrt(2) = ^?(1 (1/2+(cos(6 t))/2))/(sqrt(2))-1/sqrt(2) (1-cos(6 t))/2
(1-cos(6 t))/2 = 1/2-1/2 cos(6 t):
(cos(6 t))/sqrt(2) = ^?(1 (1/2+(cos(6 t))/2))/(sqrt(2))-1/sqrt(2) 1/2-(cos(6 t))/(2)
(1 (1/2+(cos(6 t))/2))/(sqrt(2)) = 1/(2 sqrt(2))+(cos(6 t))/(2 sqrt(2)):
(cos(6 t))/sqrt(2) = ^?(1)/(2 sqrt(2))+(1)/(2 sqrt(2)) cos(6 t)-(1 (1/2-(cos(6 t))/(2)))/(sqrt(2))
-(1 (1/2-(cos(6 t))/(2)))/(sqrt(2)) = (cos(6 t))/(2 sqrt(2))-1/(2 sqrt(2)):
(cos(6 t))/sqrt(2) = ^?(1)/(2 sqrt(2))+(1)/(2 sqrt(2)) cos(6 t)+(cos(6 t))/(2 sqrt(2))-(1)/(2 sqrt(2))
(1)/(2 sqrt(2))+cos(6 t) (1)/(2 sqrt(2))-(1)/(2 sqrt(2))+cos(6 t) (1)/(2 sqrt(2)) = (cos(6 t))/sqrt(2):
(cos(6 t))/sqrt(2) = ^?(cos(6 t))/sqrt(2)
The left hand side and right hand side are identical:
Answer: | (identity has been verified)