Take note that the reciprocal of cosine is secant.
`sec theta =1/costheta`
And the reciprocal of secant is cosine.
`cos theta =1/sec theta`
So to solve for the value of cosine given the value of secant, apply the formula above.
Plug-in `secx=sqrt5` .
Since there is a square root at the denominator, we have to rationalize the denominator to simplify it.
Thus, when `secx=sqrt5` , the value of cos x is `sqrt5/5` .