Answer
See solution
Work Step by Step
Every vector in Span{u,v} has the form $w=c_1u+c_2v$. Because y is orthogonal to both u and v, $y^T u=0$ and $y^T v=0$. Therefore, $y\cdot (c_1u+c_2v)=c_1y\cdot u+c_2y\cdot v=0+0=0$, which means y is orthogonal to each vector in the span.
