# Let A = [[a, b],[c, d]]be a 2x2 matrix. Let vector v = <a,b> and vector w = <c,d> be the column vectors of A.Conclude that A is invertible exactly when its columns vector v and vector w...

Let

A = [[a, b],[c, d]]

be a 2x2 matrix. Let vector v = <a,b> and vector w = <c,d> be the column vectors of A.

Conclude that A is invertible exactly when its columns vector v and vector w are not parallel.

sciencesolve | Teacher | (Level 3) Educator Emeritus

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You need to use the equation that relates two parallel vectors, such that:

`bar v || bar w <=> a/c = b/d => ad = bc => ad - bc = 0`

You need to prove that matrix A is invertible if the vectors are not parallel.

You should remember that a matrix is invertible if `det A != 0` , hence, evaluating the determinant of matrix A, yields:

`det A = [(a,c),(b,d)] ` `=> det A = ad - bc`

You need to notice that `det A != 0` if `ad - bc != 0` , hence, since `ad - bc != 0` , then the vector `bar v = <a,b>` is not parallel to `bar w = <c,d>` .

pramodpandey | College Teacher | (Level 3) Valedictorian

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We wish to prove that  A is invertible ,if  columns vector v and vector w are not parallel i.e cross product of  vector v and vector w  does not vanish.

`v xxw =|[a,b],[c,d]|`