theorem Th51:
  for n being Nat
  for a being Real
  for M being Matrix of n,REAL
  for x being FinSequence of REAL st n > 0 & len x = n holds
  a * (M * x) = (a * M) * x
  proof
    let n be Nat;
    let a be Real;
    let M be Matrix of n,REAL;
    let x be FinSequence of REAL;
    assume that
A1: n > 0 and
A2: len x = n;
    width M = n by MATRIX_0:24;
    then M * (a * x) = a * (M * x) by A1,A2,MATRIXR1:59;
    hence thesis by A1,A2,Th50;
  end;
