18.4    b) 3*{{1,2,3},{-1,2,5}}+2*Transpose[{{1,2,3},{-1,2,5}}]
        d) -{{1},{2},{1}}+2*Transpose[{{-3,4,5,6}}]
        e) {{1,6},{3,5},{4,7}} + {{1,2,3},{-1,2,5}}
        g) Transpose[{{1,6},{3,5},{4,7}}] - {{1,2,3},{-1,2,5}}
        j) {{1,2,3,4},{4,3,2,1},{5,7,8,9}} - {{1,0,0},{0,1,0},{0,0,1}}
	
18.5    a) {{1,6},{3,5},{4,7}}.{{1,2,3},{-1,2,5}}
        b) {{1,2,3},{-1,2,5}}.{{1,6},{3,5},{4,7}}
        c) Transpose[{{1,6},{3,5},{4,7}}].{{1,2,3},{-1,2,5}}
        f) {{1,0,0},{0,1,0},{0,0,1}}.{{1,2,3,4},{4,3,2,1},{5,7,8,9}}
        k) Transpose[{{0,0,0},{0,0,0}}].{{1,2,3},{-1,2,5}}
        l) Transpose[{{1,6},{3,5},{4,7}}].{{0,0},{0,0}}

18.7    a) {{1,2,3},{0,1,1},{0,0,-1}}.{{1,-1,-1},{0,1,1},{0,0,1}}
        b) {{1,-1,-1},{0,1,1},{0,0,1}}.{{1,2,3},{0,1,1},{0,0,-1}}
        c) {{1,-1,-1},{0,1,1},{0,0,1}}^2 - {{1,2,3},{0,1,1},{0,0,-1}}^2
        d) ({{1,-1,-1},{0,1,1},{0,0,1}} - {{1,2,3},{0,1,1},{0,0,-1}}).({{1,-1,-1},{0,1,1},{0,0,1}} - {{1,2,3},{0,1,1},{0,0,-1}})

18.9    {{0,2},{0,0}}.{{3,1},{2,0}} - {{0,2},{0,0}}.{{6,3},{2,0}}

18.10   b) {{1,6},{3,5},{4,7}}.{{1,0,0},{0,1,0},{0,0,1}}.{{1,2,3},{-1,2,5}}+4*{{1,0,0},{0,1,0},{0,0,1}}^T
        d) {{1,6},{3,5},{4,7}}^T*{{1,0,0},{0,1,0},{0,0,1}}^6*{{1,6},{3,5},{4,7}}-1/2*({{1,2,3},{-1,2,5}}*{{1,0,0},{0,1,0},{0,0,1}}^4*{{1,2,3},{-1,2,5}}^T)+{{3,4},{5,6}}^2 
        e) {{1,0},{0,2}}.{{1,2,3},{-1,2,5}}.{{1,6},{3,5},{4,7}}-{{1,0},{0,2}}.{{3,4},{5,6}}.{{1,6},{3,5},{4,7}}
        h) 2*{{1,0},{0,2}}.{{1,2,3},{-1,2,5}}.{{1,0,0},{0,1,0},{0,0,1}}.{{1},{2},{-1}}+{{3,4},{5,6}}.{{1,2,3},{-1,2,5}}.{{1},{2},{-1}}
        n) {{0,0},{0,0}}.{{1,2,3},{-1,2,5}} - Transpose[{{1,6},{3,5},{4,7}}].{{0,0,0},{0,0,0}}
        o) {{1,0},{0,2}}.{{1,6},{3,5},{4,7}}+{{1,6},{3,5},{4,7}}.{{3,4},{5,6}}
        p) {{3,4},{5,6}}.{{1,2,3},{-1,2,5}}+10*{{1,0},{0,2}}.Transpose[{{1,6},{3,5},{4,7}}]
        s) 4*{{3,4},{5,6}}.{{0,0},{0,0}}-{{0,0,0},{0,0,0}}.{{1,6},{3,5},{4,7}}

18.11   e) Transpose[Transpose[{{3,4},{5,6}}]-Transpose[{{1,0},{0,2}}]] - ({{3,4},{5,6}} - {{1,0},{0,2}})
        f) Transpose[Transpose[{{1,6},{3,5},{4,7}}]-{{1,2,3},{-1,2,5}}] - ({{1,6},{3,5},{4,7}}-Transpose[{{1,2,3},{-1,2,5}}])
        m) Transpose[{{1,0},{0,2}}.{{3,4},{5,6}}] - Transpose[{{1,0},{0,2}}].Transpose[{{3,4},{5,6}}]
        o) 2*{{1,6},{3,5},{4,7}}.Transpose[{{3,4},{5,6}}-{{1,0},{0,2}}] - ({{1,6},{3,5},{4,7}}.(2*Transpose[{{3,4},{5,6}}])-2*{{1,6},{3,5},{4,7}}.Transpose[{{1,0},{0,2}}])
        p) Transpose[2*{{-3,4,5,6}}].Transpose[{{1},{2},{-1}}] - 2*Transpose[{{1},{2},{-1}}].Transpose[{{-3,4,5,6}}]
        x) Transpose[{{-3,4,5,6}}].(3*Transpose[{{1},{2},{-1}}])-3*Transpose[{{1},{2},{-1}}.{{-3,4,5,6}}]s