Please help with a full explanation.

X 5. Let G = be a block matrix where A and B are both 2 x 2 blocks. Show that 0 B det G = (det A) (det B) and that the characteristic polynomial of G is the product of the characteristic polynomials of A and B.6. Let Vi and V2 be subspaces of R" such that Vi C V2. Show that any vector v E R" can be uniquely written as v=a+b+c with a c Vi, beVnV2, and ce V2