For what values of x, [1 2 1] ⎛⎜⎝⎡⎢⎣120201102⎤⎥⎦⎡⎢⎣02x⎤⎥⎦⎞⎟⎠=0 ?
Given, [1 2 1] ⎛⎜⎝⎡⎢⎣120201102⎤⎥⎦⎡⎢⎣02x⎤⎥⎦⎞⎟⎠=0
⇒[1 2 1]⎡⎢⎣120201102⎤⎥⎦⎡⎢⎣02x⎤⎥⎦=0⇒[1 2 3]⎡⎢⎣0+4+00+0+x0+0+2x⎤⎥⎦=0
(because Matrix multiplication is associative)
⇒[1 2 3]⎡⎢⎣4x2x⎤⎥⎦=0⇒[4+2x+2x]=0⇒4+4x=0⇒x=−1.