Calculus 3 : Vectors and Vector Operations

Study concepts, example questions & explanations for Calculus 3

varsity tutors app store varsity tutors android store

Example Questions

Example Question #751 : Vectors And Vector Operations

Find the determinant of the 3x3 matrix \(\displaystyle \begin{bmatrix} 1&0 &1 \\ 12&2 &4 \\ 5&10 &3 \end{bmatrix}\)

Possible Answers:

\(\displaystyle 76\)

\(\displaystyle 100\)

\(\displaystyle 95\)

\(\displaystyle 82\)

Correct answer:

\(\displaystyle 76\)

Explanation:

To find the determinant of a 3x3 matrix \(\displaystyle M=\begin{bmatrix} x&y &z \\ a_1&a_2 &a_3 \\ b_1& b_2&b_3 \end{bmatrix}\), you use the formula 

\(\displaystyle determinant(M)=x(a_2b_3-b_2a_3)-y(a_1b_3-b_1a_3)+z(a_1b_2-b_1a_2)\)

Using the matrix from the problem statement, we get

\(\displaystyle 1(6-40)-0(36-20)+1(120-10)=76\)

Example Question #752 : Vectors And Vector Operations

Find the determinant of the matrix \(\displaystyle \begin{bmatrix} \hat{i}&\hat{j} &\hat{k} \\ 1&-5 &3 \\ 2& 7& 0 \end{bmatrix}\)

Possible Answers:

\(\displaystyle \left \langle -20,6,14\right \rangle\)

\(\displaystyle \left \langle -21,6,17\right \rangle\)

\(\displaystyle \left \langle -21,9,17\right \rangle\)

\(\displaystyle \left \langle -21,-6,17\right \rangle\)

Correct answer:

\(\displaystyle \left \langle -21,6,17\right \rangle\)

Explanation:

To find the determinant of a 3x3 matrix \(\displaystyle m=\begin{bmatrix} x& y & z\\ a_1&a_2 &a_3 \\ b_1& b_2& b_3 \end{bmatrix}\), we use the formula 

\(\displaystyle determinant(m)=x(a_2b_3-b_2a_3)-y(a_1b_3-b_1a_3)+z(a_1b_2-b_1a_2)\)

Using the matrix from the problem statement, we get

\(\displaystyle \hat{i}(0-21)-\hat{j}(0-6)+\hat{k}(7+10)=\left \langle -21,6,17\right \rangle\)

Example Question #753 : Vectors And Vector Operations

Calculate the determinant of Matrix \(\displaystyle A\).

\(\displaystyle A=\begin{bmatrix} 1 & 2&3 \\ 0& 2& 1\\ 3& 4& 5 \end{bmatrix}\)

Possible Answers:

\(\displaystyle \det(A)=-2\)

\(\displaystyle \det(A)=6\)

\(\displaystyle \det(A)=1\)

\(\displaystyle \det(A)=-6\)

\(\displaystyle \det(A)=0\)

Correct answer:

\(\displaystyle \det(A)=-6\)

Explanation:

In order to find the determinant of \(\displaystyle A\), we first need to copy down the first two columns into columns 4 and 5. 

\(\displaystyle A=\begin{bmatrix} 1 & 2&3 & 1 &2\\ 0& 2& 1&0 &2\\ 3& 4& 5 &3 &4\end{bmatrix}\)

The next step is to multiply the down diagonals. 

\(\displaystyle A_d=1\cdot2\cdot5+2\cdot1\cdot 3+3\cdot0\cdot4=10+6+0=16\)

The next step is to multiply the up diagonals.

\(\displaystyle A_u=3\cdot2\cdot3+4\cdot1\cdot1+5\cdot0\cdot2=18+4=22\)

The last step is to substract \(\displaystyle A_u\) from \(\displaystyle A_d\).

\(\displaystyle \det(A)=A_d-A_u=16-22=-6\)

Example Question #754 : Vectors And Vector Operations

Calculate the determinant of Matrix \(\displaystyle A\).

\(\displaystyle A=\begin{bmatrix} 1 & 2&3 \\ 0& 2& 1\\ 3& 4& 5 \end{bmatrix}\)

Possible Answers:

\(\displaystyle \det(A)=0\)

\(\displaystyle \det(A)=6\)

\(\displaystyle \det(A)=-2\)

\(\displaystyle \det(A)=-6\)

\(\displaystyle \det(A)=1\)

Correct answer:

\(\displaystyle \det(A)=-6\)

Explanation:

In order to find the determinant of \(\displaystyle A\), we first need to copy down the first two columns into columns 4 and 5. 

\(\displaystyle A=\begin{bmatrix} 1 & 2&3 & 1 &2\\ 0& 2& 1&0 &2\\ 3& 4& 5 &3 &4\end{bmatrix}\)

The next step is to multiply the down diagonals. 

\(\displaystyle A_d=1\cdot2\cdot5+2\cdot1\cdot 3+3\cdot0\cdot4=10+6+0=16\)

The next step is to multiply the up diagonals.

\(\displaystyle A_u=3\cdot2\cdot3+4\cdot1\cdot1+5\cdot0\cdot2=18+4=22\)

The last step is to substract \(\displaystyle A_u\) from \(\displaystyle A_d\).

\(\displaystyle \det(A)=A_d-A_u=16-22=-6\)

Learning Tools by Varsity Tutors