cot²x - cos²x = cot²xcos²x

cos^2x/sin^2x - cos^2x=cos^2x/sin^2x cos^2x

devide by cos^2x , => 1/sin^2x - 1 = cos^2x/sin^2x

=> 1-sin^2x = cos^2x

= cos^2x+sin^2x = 1 => 1=1 ... i cant understand the point from this simplification !!! check again your question , the first one will be similar