Write the first trigonometric function in terms of the second for θ in the given quadrant ... sec θ, sin θ; θ in quadrant I

We have sec = 1/cos

Then we also have cos^2 = 1 - sin^2

Also we have cos = sqrt (1 - sin^2)

Substitute the derived cosine function to sec then we have

Sec = 1 / (sqrt (1-sin^2)