Answer:
See Explanation Below
Step-by-step explanation:
Given
[tex](sin x - cos x)^2 = sec^2x - tan^2x - 2sinx.cos x.[/tex]
Required
Prove
To start with; we open the bracket on the left hand side
[tex](sin x - cos x)^2 = (sin x - cos x)(sin x - cos x)[/tex]
[tex](sin x - cos x)^2 = (sin x )(sin x - cos x)- (cos x)(sin x - cos x)[/tex]
[tex](sin x - cos x)^2 = sin^2 x -sinx cos x - sin xcos x + cos^2 x[/tex]
[tex](sin x - cos x)^2 = sin^2 x -2sinx cos x + cos^2 x[/tex]
Reorder
[tex](sin x - cos x)^2 = sin^2 x + cos^2 x - 2sinx cos x[/tex]
From trigonometry;
[tex]sin^2x + cos^2x = 1[/tex]
So;
[tex](sin x - cos x)^2 = sin^2 x + cos^2 x - 2sinx cos x[/tex]
becomes
[tex](sin x - cos x)^2 = 1 - 2sinx cos x[/tex]
Also from trigonometry;
[tex]sec^2x - tan^2x = 1[/tex]
So,
[tex](sin x - cos x)^2 = 1 - 2sinx cos x[/tex]
becomes
[tex](sin x - cos x)^2 = sec^2x - tan^2x - 2sinx cos x[/tex]
Proved
