In: Math
10. Assume k is a scalar and A is a m × n matrix. Show that if kA = 0 then either k = 0 or A = 0m x n
Here, k is a scalar and A is a mxn matrix.
Then, A = 
 is a mxn matrix.
Now, kA = k
= 
Given kA = O
i.e., 
 = 
i.e., kaij = 0, where 1 
 i 
 m and 1 
 j 
 n.
which implies either k = 0 or aij = 0.
[Since we know that product of two numbers is 0 implies that one of them must be 0]
Now, aij = 0 for 1 
 i 
 m, 1 
 j 
 n implies 
 = 
i.e., A = 
.
Therefore, if kA = 0 then either k = 0 or A = 0mxn.