Question

Prove that Q is orthogonal. (This procedure gives a quick method for finding an orthonormal basis for Rn with a prescribed first vector x, a construction that is frequently useful in applications).
where x is a one column matrix of 2 rows (x1 and y)
and Q is 2x2 matrix, in the first column (x1 and y transpose) and in the second column (y and I-(1/(1-x1)yy^T)
please I need brief answer, Thank you