5.1     a) 3*4*sin(pi*3)
        b) 7*5*sin(arccos(-21/(7*5)))
	c) 3*6*sin(0)

5.2     CrossProduct[{2,-3,1},{5,1,-2}]
        CrossProduct[3*{2,-3,1}-2*{5,1,-2},{2,-3,1}+5*{5,1,-2}]

5.3     a) CrossProduct[{2,2,11},{-2,2,5}]
        b) CrossProduct[{1,-3,2},{-3,-1,-4}]

5.4     1/2*(3*0-4*0+(2+6)*6*6*sin(pi/4))

5.5     |-3*0-2*0+(1-6)*5*4*sin(pi/6)|

5.6     {1,2}.{2,-1}
        ||{1,2}|| - ||{2,-1}||
        CrossProduct[1/sqrt(5)*{1,2, 0},{2,-1, 0}]

5.7     CrossProduct[{2,3,-1},{1,-1,3}]    *(-1)

5.8     CrossProduct[-1/(25*sqrt(5))*{11,10,2},{4,0,3}]

5.9     a) CrossProduct[{1,0,0},{1,-5,-2}]
        b) CrossProduct[{0,0,1},{2,5,7}]

5.10    a) CrossProduct[{1,4,1},{3,-2,1}]
           -(0+4*0+0)
        b) CrossProduct[{2,1,1},{-4,-3,-1}]
           -(-1-7-(-6))
        c) CrossProduct[{1,0,-3},{-1,1,0}]
           -(2*3+0*3+2*1)

5.11    solve 5x-z+3=0, 2x-y-4z+5=0, 3y+2z-1=0

5.12    -(1*1-2*(-2)+3*1)