Q29. - Algebra 2

Question

Use$A=\left[\begin{array}{cc}1& -2\\ 4& 3\end{array}\right]$ , $B=\left[\begin{array}{cc}-5& 2\\ 4& 3\end{array}\right]$, and  $C=\left[\begin{array}{cc}5& 1\\ 2& -4\end{array}\right]$ and scalar $c=3$ to determine whether the equation is true for the given matrices.

$C(A+B)=AC+BC$

Step-by-Step Solution

Answer

The provided equation is false.

Step 1- Determine the value of C ( A + B )

Substitute the provided matrices into $C(A+B)$

$C(A+B)=\left[\begin{array}{cc}5& 1\\ 2& -4\end{array}\right](\left[\begin{array}{cc}1& -2\\ 4& 3\end{array}\right]+\left[\begin{array}{cc}-5& 2\\ 4& 3\end{array}\right])$

First perform the addition after it multiply the resulting matrix with C. 

$\begin{array}{c}C(A+B)=\left[\begin{array}{cc}5& 1\\ 2& -4\end{array}\right]\cdot \left[\begin{array}{cc}-4& 0\\ 8& 6\end{array}\right]\\ =\left[\begin{array}{cc}1& 1\\ 10& 2\end{array}\right]\end{array}$

Step 2 – Determine the value of A C + B C

Substitute the provided matrices into $AC+BC$

$AC+BC=\left[\begin{array}{cc}1& -2\\ 4& 3\end{array}\right]\cdot \left[\begin{array}{cc}5& 1\\ 2& -4\end{array}\right]+\left[\begin{array}{cc}-5& 2\\ 4& 3\end{array}\right]\cdot \left[\begin{array}{cc}5& 1\\ 2& -4\end{array}\right]$

First perform the multiplication between the matrices after it perform addition betwee the resulting matrices. 

$\begin{array}{c}AC+BC=\left[\begin{array}{cc}1& 9\\ 26& -8\end{array}\right]+\left[\begin{array}{cc}-21& -13\\ 26& -8\end{array}\right]\\ =\left[\begin{array}{cc}-20& -4\\ 52& -16\end{array}\right]\end{array}$

Step 3- Make the conclusion

As both the sides are not resulting in same matrix which means that the provided equation is false.