Answer: 2sin^2x+sin2x+cos2x=0 ..... (1).
By using the trigonometric identities below :
sin2x=2sinxcosx
cos2x=cos^2x-sin^2x
We substitute the trigonometric identities into (1).
2sin^2x+2sinxcosx+cos^2x-sin^2x=0
By combining like terms .
sin^2x+2sinxcosx+cos^2x=0.....(2)
The equation (2) is equivalent to the following expression (3).
(sinx+cosx)(sinx+cosx)=0 .....(3).
sinx+cosx=0
cosx=-sinx
divide both sides by cosx
1=-sinx/cosx
-1=sinx/cosx
sinx/cosx=tanx
substitute
-1=tanx
tanx=-1
tangent is negative in 2nd and 4th quadrants
tan135º=-1 (one answer)
tan315º=-1 (second answer)
Explanation:
Please refer to the trigonometric identities used and explained above .