$$\cos^2x=\cot^2x-\frac{\cos^2x}{\tan^2x}$$
How can I solve it?
$$\cos^2x=\frac{\sin^2x}{\tan^2x}\\ \sin^2x=1-\cos^2x\\ \frac{\sin^2x}{\tan^2x}=\frac{1-\cos^2x}{\tan^2x}\\ \frac{1-\cos^2x}{\tan^2x}=\frac{1}{\tan^2x}-\frac{\cos^2x}{\tan^2x}\\ \cos^2x=\cot^2x-\frac{\cos^2x}{\tan^2x}$$
$$\cot^2x-\frac{\cos^2x}{\tan^2x}=\frac{1}{tan^2x}-\frac{\cos^2x}{\tan^2x}=\frac{sin^2x}{tan^2x}=cos^2x $$
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$$\cos^2x=\frac{\sin^2x}{\tan^2x}\\ \sin^2x=1-\cos^2x\\ \frac{\sin^2x}{\tan^2x}=\frac{1-\cos^2x}{\tan^2x}\\ \frac{1-\cos^2x}{\tan^2x}=\frac{1}{\tan^2x}-\frac{\cos^2x}{\tan^2x}\\ \cos^2x=\cot^2x-\frac{\cos^2x}{\tan^2x}$$