√200*cos²5π\8-√50 выручите пожалуйста

[latex] \sqrt{200}* cos^{2} \frac{ \pi }{8} - \sqrt{50} = \sqrt{50}*( \sqrt{4}* cos^{2} \frac{5 \pi }{8} -1) = \sqrt{50} *(2cos^{2} \frac{5 \pi }{8}-1 )[/latex] [latex]= \sqrt{25*2} *cos(2* \frac{5 \pi }{8} )=5 \sqrt{2} *cos \frac{5 \pi }{4} =5 \sqrt{2} *cos( \pi + \frac{ \pi }{4} )=[/latex] [latex]=5 \sqrt{2} *(-cos \frac{ \pi }{4} )=5 \sqrt{2} *(- \frac{ \sqrt{2} }{2} )=-5[/latex]