A= 3i + 4j+ 12k
B= 12j - 9k
question
a. C= A-(A.B)B
b. C perpendicular to the B
+33661 a. Use the fact that i.i = j.j = k.k = 1; i.j = j.k = k.i = i.k = k.j = j.i = 0
A.B = (3i + 4j + 12k)(12j - 9k) = 36i.j - 27i.k +48j.j - 36j.k + 144k.j - 108k.k = 48 - 108 = -60
C = 3i + 4j + 12k - 60(12j - 9k) = 3i + 4j + 12k -720j + 540k = 3i -716j + 552k
b. Do you mean CxB? If so use ixi = jxj = kxk = 0; ixj = - jxi = k; jxk = -kxj = i; kxi = - ixk = j
