Multiplying a determinant by a constant? book says

[mr_coffee]

I'm confused, this question had 5 parts and i got the other 4 but this one I keep missing...
If A is a 2x2 matrix...
Det(A) = -5;
The Det(-3A);
The book said, if u multiply a column by a constant k then the determinant is also multiplied by k. So wouldn't the answer just be (-5)(-3) = 15?
Det(-3A) = 15? it says its wrong htough...

 

[robphy]

Evaluate \left|\begin{array}{cc} ka& kb \\ kc&kd\end{array}\right|... and compare it to \left|\begin{array}{cc} a& b \\ c&d\end{array}\right|. Next try the 3x3 case.