Chapter 2 - Acute Angles and Right Triangles - Section 2.3 Finding Trigonometric Function Values Using a Calculator - 2.3 Exercises - Page 64: 46

Since $a$ is multiplied by $\cos$ $\theta$ the result will always be less that $a$.

$\cos$ $\theta$ = $\frac{r}{a}$ Therefore: $r$ = $a$ $\cos$$\theta$ Since the angle of offset($\theta$) exists between 0$^{\circ}$ and 90$^{\circ}$, $\cos$ $\theta$ will always be less than or equal to 1. Since $a$ is multiplied by $\cos$ $\theta$ the result will always be less that $a$.