Answer
$cos\theta$
Work Step by Step
Use the identities $sec\theta=\frac{1}{cos\theta}$ and $tan\theta=\frac{sin\theta}{cos\theta}$, we have $sec\theta-sin\theta\ tan\theta=\frac{1}{cos\theta}-sin\theta\times\frac{sin\theta}{cos\theta}=\frac{1-sin^2\theta}{cos\theta}=\frac{cos^2\theta}{cos\theta}=cos\theta$
