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Vectors and matrices — ACT practice questions

Practice 45 Vectors and matrices questions in the app

What this topic is

Vectors and matrices on the ACT Mathematics test covers vector length, matrix equality, and using given entries to find a related value.

A student has to compute magnitude from components, recognize when two matrices are the same, and combine named entries after a simple operation. The exam tends to ask for the magnitude of a vector, which matrix equals a given expression, or a value such as a plus b.

Answer choices are usually numbers or small matrices. Common traps include swapping components, treating matrix multiplication as commutative, and choosing a matrix with the right entries in the wrong order.

Sample questions

Pick an answer to see whether it is right — nothing is saved, and nothing needs an account.

Question 1Easier

What is the magnitude of the vector 6,8\langle -6, 8 \rangle?

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Answer: B — 10

Magnitude is (6)2+82=36+64=100=10\sqrt{(-6)^2 + 8^2} = \sqrt{36 + 64} = \sqrt{100} = 10.

Question 2Easier

Which of the following matrices is equal to 3[2005][3102]3\begin{bmatrix}2 & 0 \\ 0 & 5\end{bmatrix}-\begin{bmatrix}3 & 1 \\ 0 & 2\end{bmatrix}?

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Answer: A — [31013]\begin{bmatrix}3 & -1 \\ 0 & 13\end{bmatrix}

Scale first: 3[2005]=[60015]3\begin{bmatrix}2 & 0 \\ 0 & 5\end{bmatrix}=\begin{bmatrix}6 & 0 \\ 0 & 15\end{bmatrix}. Subtracting entry by entry gives 63=36-3=3, 01=10-1=-1, 00=00-0=0, and 152=1315-2=13.

Question 3Mid

If [1201][ab]=[73]\begin{bmatrix}1 & 2 \\ 0 & 1\end{bmatrix}\begin{bmatrix}a \\ b\end{bmatrix}=\begin{bmatrix}7 \\ 3\end{bmatrix}, what is the value of a+ba+b?

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Answer: C — 4

The second row gives b=3b=3. Then a+2b=7a+2b=7, so a=1a=1 and a+b=4a+b=4.

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Practice 45 Vectors and matrices questions in the app

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