Let $A,A'$ two affine subspaces of a finite Euclidean Vectorspace $V$. Let $p,p'$ two points, such that $d(A,p)=d(A',p')$. $\dim(A)=\dim(A')$
I would like to show that there exists a movement $\alpha:V->V$ such that $\alpha(A)=A'$ and $\alpha(p)=p'$
I only know, if $\alpha$ is a movement, then the following properties hold:
(1) $d(\alpha(v),\alpha(w))=d(v,w)$
(2) $\alpha$ is affine
(3) $\alpha$ affine and for a basis $a_1,..,a_n$ it holds that $d(\alpha(a_i),\alpha(a_j))=d(a_i,a_j)$
How can I use this to prove the statement above ?
Affine functions are just compostions of translations and linear transformations. So you may just adhere some translations to an orthogonal transformation to achieve your goal.
Specifically, take an orthonormal basis $\{u_1,\ldots,u_m\}\ (m=\dim A)$ of $A$ and an orthonormal basis $\{v_1,\ldots,v_m\}$ of $A'$. Complete them to two orthonormal bases $\{u_1,\ldots,u_n\}\ (n=\dim V)$ and $\{v_1,\ldots,v_n\}$ of $V$. For any $x\in V$, define $\alpha(x) = p' + \sum_i \lambda_iv_i$ whenever $x-p=\sum_i \lambda_iu_i$. Now you are done.