[tex]\displaystyle\bf\\Cos\alpha =\frac{11}{43}\\\\\\Cos^{2} \frac{\alpha }{2} =\frac{1+Cos\alpha }{2} =\frac{1+\dfrac{11}{43} }{2} =\frac{54}{43} :2=\frac{54}{86} =0,628\\\\\\Otvet \ : \ Cos^{2} \frac{\alpha }{2}=\frac{1+\dfrac{11}{43} }{2} =0,628[/tex]