Answer:
see explanation
Step-by-step explanation:
[tex]\frac{3\pi }{4}[/tex] is an angle in the second quadrant where sin > 0 and cos < 0
cos([tex]\frac{3\pi }{4}[/tex] )
= cos (π - [tex]\frac{3\pi }{4}[/tex] )
= - cos ([tex]\frac{\pi }{4}[/tex] )
= - [tex]\frac{\sqrt{2} }{2}[/tex]
and similarly
sin ([tex]\frac{3\pi }{4}[/tex] )
= sin ([tex]\frac{\pi }{4}[/tex] )
= [tex]\frac{\sqrt{2} }{2}[/tex]
