21. let a be a 4 x 4 matrix with real entries such that-1, 1, 2,-2 are its eigen values. if b a-542+51, where denotes the 4x 4 identity matrix, then which of th

21. Let A be a 4 x 4 matrix with real entries such that-1, 1, 2,-2 are its eigen values. If B A-542+51, where denotes the 4x 4 identity matrix, then which of the following statements are correct? (a) det(4 +B) = 0 (b) det(B)=1 (c) trace of A - B is 0(d) trace of A + B is 4