Worksheet on Matrix Multiplication

Practice the questions given in the Worksheet on Matrix Multiplication.

1. Let A = $\begin{bmatrix} -10 & 1\\ 3 & -2 \end{bmatrix}$, B = $\begin{bmatrix} 6\\ -7 \end{bmatrix}$. Find AB and BA if possible.

2. Let A = $\begin{bmatrix} 1 & -1\\ 3 & 4 \end{bmatrix}$, B = $\begin{bmatrix} 0 & 1\\ 2 & -3 \end{bmatrix}$.

(i) Find AB and BA if possible.

(ii) Verify if AB = BA.

(iii) Find A².

(iv) Find AB².

3. If A = $\begin{bmatrix} sin \, \, 30^{\circ} + cos \, \, 60^{\circ} & tan \, \, 45^{\circ} - cot \, \, 45^{\circ}\\ cos \, \, 90^{\circ} & sin \, \, 90^{\circ} \end{bmatrix}$ then prove that A³ = A² =A.

4. If A = $\begin{bmatrix} cos \, \, \theta & -sin \, \, \theta\\ sin \, \, \theta & cos \, \, \theta \end{bmatrix}$ and B = $\begin{bmatrix} cos \, \, \theta & sin \, \, \theta\\ -sin \, \, \theta & cos \, \, \theta \end{bmatrix}$, then prove that AB = I, where I is the unit matrix.

5. Let A = $\begin{bmatrix} -2 & 9\\ 1 & 3 \end{bmatrix}$, B = $\begin{bmatrix} 1 & 1\\ 1 & 1 \end{bmatrix}$ and C = $\begin{bmatrix} -1 & 2\\ 3 & -1 \end{bmatrix}$.

(i) Find (AB)C.

(ii) Prove that A(BC) = (AB)C.

Answer:

1. AB = $\begin{bmatrix} -67\\ 32 \end{bmatrix}$; BA is not possible because number of columns in B ≠ number of rows in A

2. (i) AB = $\begin{bmatrix} -2 & 4\\ 8 & -9 \end{bmatrix}$; B = $\begin{bmatrix} 3 & 4\\ -7 & -14 \end{bmatrix}$

(ii) AB ≠ BA.

(iii) $\begin{bmatrix} -2 & -5\\ 15 & 13 \end{bmatrix}$

(iv) $\begin{bmatrix} 8 & -14\\ -18 & 35 \end{bmatrix}$

5. (i) $\begin{bmatrix} 14 & 7\\ 8 & 4 \end{bmatrix}$

10th Grade Math

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