+0  
 
0
45
1
avatar

Let a and b be three-dimensional vectors. Then \((5a + 7 b) \times (-a+ 3 b) = ka \times b\)
for some scalar k. Find k.

 Apr 29, 2020
 #1
avatar+30086 
+3

The cross-product of a vector with itself is zero, so the LHS reduces to:  15(a x b) - 7(b x a)  =  15(a x b) + 7(a x b) = 22(a x b)

 

So k = 22

.

 Apr 29, 2020

14 Online Users