Solution
= Solution
The two <derivatives> are $2x$ and $2(x-1)$. At the intersection their slopes are $1$ and $-1$, so their direction <vectors> $(1,1)$ and $(1,-1)$ have zero <dot product>. Thus the <tangent lines> are perpendicular and their angle is
$$
\boxed{\frac\pi2\ \text{radians}=90^\circ.}
$$