Answer:
[tex]Fourth \: option: y^2=9^2+19^2-2(9)(19) cos(41°)[/tex]
[tex]The \: law \: of \: cosines \: to \: solve \: for \: one \: side \: is:[/tex]
[tex]c^2=a^2+b^2-2ab \: cos \: C[/tex]
We must know the other two sides (a and b) and the angle between these sides (angle C, the opposite to the side that we want to determine)
In this case c=y, a=9, b=19, and C=41°, then:
[tex]y^2=9^2+19^2-2(9)(19) \: cos \: (41°)[/tex]
