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Na podstawie wykresu funkcji:

$\text{a)}\cos \left(\frac{3\pi }{4}\right)=-\frac{\sqrt{2}}{2}$  

$\text{b)}\cos \left(-\frac{\pi }{4}\right)=\frac{\sqrt{2}}{2}$  

$\text{c)}\cos \left(-\frac{3\pi }{4}\right)=-\frac{\sqrt{2}}{2}$  

$\text{d)}\cos \left(\frac{5\pi }{4}\right)=-\frac{\sqrt{2}}{2}$