Answer:
The value of cos 0 = - 2 sqrt(85) / 85 = - 0.216930458
Explanation:
cos 0 = ?
Point on the terminal side of 0 : (-2,9)=(x,y)→x=-2, y=9
cos 0 = x/r
r=sqrt(x^2+y^2)
Replacing the known values:
r=sqrt( (-2)^2+(9)^2)
r=sqrt(4+81)
r=sqrt(85)
cos 0 = x/r
cos 0 = -2 / sqrt(85) = -2/9.219544457 = -0.216930458
Rationalizing:
cos 0 = -[2 / sqrt(85)] [sqrt(85) / sqrt(85)]
cos 0 = - 2 sqrt(85) / [sqrt(85)]^2
cos 0 = - 2 sqrt(85) / 85