Question

What is the value of cos 0 given that (-2,9) is a point on the terminal side of 0?

Answer 1

Answer:

The value of cos 0 = - 2 sqrt(85) /  85 = - 0.216930458

Step-by-step 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