[tex]ctg225^{o} =ctg(180^{o} +45^{o} )=ctg45^{o} =1\\\\tg120^{o} =tg(180^{o} -60^{o} )=-tg60^{o} =-\sqrt{3} \\\\\\korzystam~~ze~~wzrow:\\\\tg(180^{o} -\alpha )=-tg\alpha \\\\ctg(180^{o} +\alpha )=ctg\alpha \\\\Podstawiam:\\\\ctg225^{o} \cdot tg120^{o} =1\cdot (-\sqrt{3} )=-\sqrt{3}[/tex]
Odp: ctg225° × tg120° = -√3.
