Calculus 3 : Matrices

Study concepts, example questions & explanations for Calculus 3

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Example Questions

Example Question #131 : Matrices

Find the determinant of the 3x3 matrix \(\displaystyle \begin{bmatrix} 1& 3& -1\\ 5&0 &3 \\ -3&2 &7 \end{bmatrix}\)

Possible Answers:

\(\displaystyle 148\)

\(\displaystyle 120\)

\(\displaystyle 112\)

\(\displaystyle -148\)

Correct answer:

\(\displaystyle -148\)

Explanation:

To find the determinant of any 3x3 matrix \(\displaystyle a=\begin{bmatrix} a&b &c \\ d& e& f\\ g& h& i \end{bmatrix}\), we use the formula \(\displaystyle determinant=a(ei-hf)-b(di-gf)+c(dh-ge)\). Using the vector from the problem statement, we get \(\displaystyle 1(0-6)-3(35+9)-1(10-0)=-6-132-10=-148\)

Example Question #726 : Vectors And Vector Operations

Perform the matrix operation \(\displaystyle \begin{bmatrix} 2&1 \\ 3& 6 \end{bmatrix}-\begin{bmatrix} 0&7 \\ 1&5 \end{bmatrix}\)

Possible Answers:

\(\displaystyle \begin{bmatrix} 2&-6 \\ 2 & 4 \end{bmatrix}\)

\(\displaystyle \begin{bmatrix} 2&5 \\ 2 & 1 \end{bmatrix}\)

\(\displaystyle \begin{bmatrix} 1&-6 \\ 0& 1 \end{bmatrix}\)

\(\displaystyle \begin{bmatrix} 2&-6 \\ 2 & 1 \end{bmatrix}\)

Correct answer:

\(\displaystyle \begin{bmatrix} 2&-6 \\ 2 & 1 \end{bmatrix}\)

Explanation:

To find the difference between two 2x2 matrices \(\displaystyle a=\begin{bmatrix} a& b\\ c&d \end{bmatrix}\) and \(\displaystyle b=\begin{bmatrix} e& f\\ g& h \end{bmatrix}\) you use the formula \(\displaystyle a-b=\begin{bmatrix} a-e&b-f \\ c-g& d-h \end{bmatrix}\). Using the two matrices from the problem statement, we then get \(\displaystyle \begin{bmatrix} 2-0& 1-7\\ 3-1& 6-5 \end{bmatrix}=\begin{bmatrix} 2&-6 \\ 2& 1 \end{bmatrix}\)

Example Question #722 : Vectors And Vector Operations

Perform the matrix operation \(\displaystyle \begin{bmatrix} 4&x \\ z& 5 \end{bmatrix}-\begin{bmatrix} 1&5x \\ 3z&7 \end{bmatrix}\)

Possible Answers:

\(\displaystyle \begin{bmatrix} -4&3x \\ z&6 \end{bmatrix}\)

\(\displaystyle \begin{bmatrix} 3&-4x \\ -2z&-2 \end{bmatrix}\)

\(\displaystyle \begin{bmatrix} 7&3x \\ -2z&0 \end{bmatrix}\)

\(\displaystyle \begin{bmatrix} 1&x \\ -3z&5 \end{bmatrix}\)

Correct answer:

\(\displaystyle \begin{bmatrix} 3&-4x \\ -2z&-2 \end{bmatrix}\)

Explanation:

To find the difference between two 2x2 matrices \(\displaystyle a=\begin{bmatrix} a& b\\ c&d \end{bmatrix}\) and \(\displaystyle b=\begin{bmatrix} e& f\\ g& h \end{bmatrix}\) you use the formula \(\displaystyle a-b=\begin{bmatrix} a-e&b-f \\ c-g& d-h \end{bmatrix}\). Using the two matrices from the problem statement, we then get \(\displaystyle \begin{bmatrix} 4-1& x-5x\\ z-3z& 5-7 \end{bmatrix}=\begin{bmatrix} 3&-4x \\ -2z& -2\end{bmatrix}\)

Example Question #132 : Matrices

Find the determinant of the 2x2 matrix \(\displaystyle \begin{bmatrix} 4& 2\\ 1&-5 \end{bmatrix}\)

Possible Answers:

\(\displaystyle -18\)

\(\displaystyle -22\)

\(\displaystyle -15\)

\(\displaystyle 15\)

Correct answer:

\(\displaystyle -22\)

Explanation:

To find the determinant of a 2x2 matrix \(\displaystyle a=\begin{bmatrix} a&b \\ c&d \end{bmatrix}\) ,we use the formula 

\(\displaystyle determinant=(ad)-(cb)\)

Using hte matrix from the problem statement, we get

\(\displaystyle determinant=(-4*5)-(1*2)=-22\) 

 

Example Question #133 : Matrices

Find the determinant of the 3x3 matrix \(\displaystyle \begin{bmatrix} i&j &k \\ 3&-4 &1 \\ 2&0 &5 \end{bmatrix}\)

Possible Answers:

\(\displaystyle \left \langle 4,-10,8\right \rangle\)

\(\displaystyle \left \langle -20,13,8\right \rangle\)

\(\displaystyle \left \langle 20,15,8\right \rangle\)

\(\displaystyle \left \langle -20,-13,8\right \rangle\)

Correct answer:

\(\displaystyle \left \langle -20,-13,8\right \rangle\)

Explanation:

To find the determinant of the 3x3 matrix \(\displaystyle \begin{bmatrix} i& j& k\\ a&b &c \\ x&y &z \end{bmatrix}\), we use the formula:

\(\displaystyle determinant=i(bz-yc)-j(az-xc)+k(ay-xb)\). Using the matrix from the problem statement, we get:

\(\displaystyle i(-20-0)-j(15-2)+k(0+8)=\left \langle -20,-13,8\right \rangle\)

Example Question #134 : Matrices

Find the determinant of the 3x3 matrix \(\displaystyle \begin{bmatrix} i&j &k \\ 2&1 &1 \\ 6&6 &7 \end{bmatrix}\)

Possible Answers:

\(\displaystyle \left \langle 2,-8,9\right \rangle\)

\(\displaystyle \left \langle 1,-8,6\right \rangle\)

\(\displaystyle \left \langle 2,1,8\right \rangle\)

\(\displaystyle \left \langle 1,8,6\right \rangle\)

Correct answer:

\(\displaystyle \left \langle 1,-8,6\right \rangle\)

Explanation:

To find the determinant of the 3x3 matrix \(\displaystyle \begin{bmatrix} i& j& k\\ a&b &c \\ x&y &z \end{bmatrix}\), we use the formula:

\(\displaystyle determinant=i(bz-yc)-j(az-xc)+k(ay-xb)\). Using the matrix from the problem statement, we get:

\(\displaystyle i(7-6)-j(14-6)+k(12-6)=\left \langle 1,-8,6\right \rangle\)

Example Question #731 : Vectors And Vector Operations

Perform the matrix operation \(\displaystyle \begin{bmatrix} 4&2 &0 &1 \\ 3&2 &1 &7 \\ 3&4 &5 &1 \\ 2&3 &0 & 5 \end{bmatrix}+\begin{bmatrix} 4&2 &8 &0 \\ 5&3 &1 &6 \\ 5&11 &10 &2 \\ 4&6 &9 &1 \end{bmatrix}\)

Possible Answers:

\(\displaystyle \begin{bmatrix} 8&4 &8 &1 \\ 8&5 &2 &13 \\ 8&15 &15 &3 \\ 6&9 &9 &6 \end{bmatrix}\)

\(\displaystyle \begin{bmatrix} 1&4 &0 &0 \\ 15&3 &1 &42 \\ 15&44 &50 &2 \\ 7&18 &0 &1 \end{bmatrix}\)

\(\displaystyle \begin{bmatrix} 1&4 &0 &0 \\ 15&6 &1 &4 \\ 15&44 &5 &2 \\ 8&8 &0 &5 \end{bmatrix}\)

\(\displaystyle \begin{bmatrix} 16&4 &0 &1 \\ 15&6 &1 &4 \\ 5&19 &50 &2 \\ 8&18 &0 &5 \end{bmatrix}\)

Correct answer:

\(\displaystyle \begin{bmatrix} 8&4 &8 &1 \\ 8&5 &2 &13 \\ 8&15 &15 &3 \\ 6&9 &9 &6 \end{bmatrix}\)

Explanation:

To do matrix summation, you apply the following formula, where a and b are 4x4 matrices: \(\displaystyle \begin{bmatrix} a&b &c &d \\ e&f &g &h \\ i&j &k &l \\ m&n & o&p \end{bmatrix}+\begin{bmatrix} q& r& s&t \\ u&v &w &x \\ y&z &a_1 &b_1 \\ c_1&d_1 &e_1 &f_1 \end{bmatrix}=\begin{bmatrix} a+q&b+r &c+s &d+t \\ e+u&f+v &g+w &h+x \\ i+y&j+z &k+a_{1} &l+b_{1} \\ m+c_{1}&n+d_{1} &o+e_{1} &p+f_{1} \end{bmatrix}\)

Using this formula, we get \(\displaystyle \begin{bmatrix} 8&4 &8 &1 \\ 8&5 &2 &13 \\ 8&15 &15 &3 \\ 6&9 &9 &6 \end{bmatrix}\)

Example Question #731 : Vectors And Vector Operations

Find the determinant of the 3x3 matrix given: \(\displaystyle \begin{bmatrix} 1&4 &7 \\ 3&7 &8 \\ 5&0 &6 \end{bmatrix}\)

Possible Answers:

\(\displaystyle -115\)

\(\displaystyle 60\)

\(\displaystyle 25\)

\(\displaystyle -100\)

Correct answer:

\(\displaystyle -115\)

Explanation:

To find the the determinant of a 3x3 matrix \(\displaystyle a=\begin{bmatrix} a& b&c \\ d&e &f \\ h&i &j \end{bmatrix}\), you apply the following formula

\(\displaystyle determinant=a(ej-if)-b(dj-hf)+c(di-he)\)

Applying to the matrix from the problem statement, we get

\(\displaystyle 1(42-0)-4(18-40)+7(0-35)=-115\)

Example Question #732 : Vectors And Vector Operations

Find the determinant of the 3x3 matrix given: \(\displaystyle \begin{bmatrix} 2&0 &4 \\ 3&1 &6 \\ 5&2 &7 \end{bmatrix}\)

Possible Answers:

\(\displaystyle -6\)

\(\displaystyle 5\)

\(\displaystyle 14\)

\(\displaystyle 6\)

Correct answer:

\(\displaystyle -6\)

Explanation:

To find the the determinant of a 3x3 matrix \(\displaystyle a=\begin{bmatrix} a& b&c \\ d&e &f \\ h&i &j \end{bmatrix}\), you apply the following formula

\(\displaystyle determinant=a(ej-if)-b(dj-hf)+c(di-he)\)

Applying to the matrix from the problem statement, we get

\(\displaystyle 2(7-12)-0(21-30)+4(6-5)=-6\)

Example Question #135 : Matrices

Find the determinant of the 2x2 matrix given: \(\displaystyle \begin{bmatrix} 3&x \\ 7&2 \end{bmatrix}\)

Possible Answers:

\(\displaystyle 6-7x\)

\(\displaystyle 6+7x\)

\(\displaystyle 3x+9\)

\(\displaystyle 2x+3\)

Correct answer:

\(\displaystyle 6-7x\)

Explanation:

To find the determinant of a 2x2 matrix \(\displaystyle a=\begin{bmatrix} x&y \\ z&q \end{bmatrix}\), we use the formula:

\(\displaystyle detemrinant=xq-zy\)

Using the vector from the problem statement, we get:

\(\displaystyle (3*2)-(7*x)=6-7x\)

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