Origins of Algebra
Algebra was described in the 9th century book (cIlm al-jabr wa l-muqābala) “The Science of Restoring and Balancing”, by the Persian mathematician al-Khwarizmi Muḥammad ibn Mūsā al-Khwārizmī. الجبر al-jabr “resetting” refers to moving a term between the sides of an equation, المقابلة al-muqābala “balancing” referred to adding equal terms to both sides. The book is full of algorithms for solving equations.
Properties of the equality \(a=b\)
Addition property of equality: |
\(a + \color{red}{c}= b + \color{red}{c}\) |
Subtraction property of equality: |
\(a - \color{red}{c} = b - \color{red}{c}\) |
Multiplicative property of equality: |
\(a \color{red}{c}= b \color{red}{c}\) |
Division property of equality: |
\(a /\color{red}{c} = b / \color{red}{c}\) |
Reciprocal property of equality: |
\(\frac{1}{a} = \frac{1}{b}\) |
Functional equivalents of equality: |
\(f(a) = f(b)\) |
Some useful properties
commutative |
\(a + b = b + a\) |
\(a b = b a\) |
associative |
\((a+b)+c = a+(b+c)\) |
\((ab)c = a(bc)\) |
distributive |
|
\(a(b+c)=ab + ac\) |
identity |
\(a+0 = a\) |
\(a\times 1 = a\) |
inverse |
\(I(a) = -a\) |
\(I(a) = \frac{1}{a}\) |
Strategy to solving equations
- Using properties of equality, migrate variables to one side and constants to the other
- The Simplify left and right sides of the equation
- Rearrange the terms
- Apply operations to both sides
- Reduce the terms to simple terms
Example of an Algebratic expression
\[\frac{x+2}{4} = \frac{x-1}{3} +2\]
Solution: Part 1
\[\eqalign{\frac{x+2}{4} \color{red}{{- \frac{x-1}{3}}} &=& \color{yellow}{\frac{x-1}{3}} + 2 \color{red}{- \frac{x-1}{3}}\cr
\color{red}{\left(\frac{3}{3}\right)}\left(\frac{x+2}{\color{yellow}{4}}\right) - \color{red}{\left(\frac{4}{4}\right)}\left(\frac{x-1}{\color{yellow}{3}}\right) &=& 2\cr
\color{red}{12}\left(\frac{3x +6}{\color{yellow}{12}} - \frac{4x-4}{\color{yellow}{12}}\right) &=& 2 \color{red}{\times 12}}\]
Solution: Part 2
\(\begin{eqnarray}\color{yellow}{(3x + 6)} - \color{yellow}{(4x-4)} &=& 24\\ \color{red}{(3x - 4x)} + \color{red}{(6 + 4)} &=& 24 \\ -x + \color{yellow}{10} \color{red}{- 10} &=& 24 \color{red}{- 10}\\ \color{red}{-1}(\color{yellow}{-x}) &=& \color{red}{-1 \times}14\\ x &=& -14 \end{eqnarray}\)
Challenges: Solve for \(x\)
\[2(x-3) - 17 = 13 - 3(x+2)\]
\[\frac{3}{x+6} + \frac{1}{x-2} = \frac{4}{x^2 + 4x -12}\] \[\frac{1}{x} + \frac{1}{q} = \frac{1}{f}\]
\[(x^2 -25)(x + 5) = 11(x-5)\]
Multiplication of polynomials
\(\eqalign{(ax+b)(cx+d) &=& (acx^2 + adx) + bcx + bd)\\ &=& acx^2 + (ad+bc)x + bd}\)
\[(x+3)(x-2) = (x^x -2x) + (3x - 6)= x^2 + x -6\]
\[(x+3)(x+3) = (x^x +3x) + (3x + 9)= x^2 + 6x + 9\] \[(x+3)(x-3) = (x^x -3x) + (3x - 9)=x^2 - 9\]
Graphically Factoring polynomials
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Given this graph of an unknown relationship what can we say about its root factors and its behavior?
Effects of order of the function
Functions that share root factors
Solving systems of equations
\[\begin{eqnarray}
y &=& \frac{x}{2} -1 \\
y &=& -2x + 1\\
\\
\frac{x}{2} -1 &=& -2x + 1\\
\frac{x}{2} -1 \color{red}{+ 2x +1}&=& -2x + 1\color{red}{+ 2x +1}\\
\left(\frac{5}{2}\right)x\color{red}{\times \frac{2}{5}} &=& 2\color{red}{\times \frac{2}{5}}\\
x &=& \frac{4}{5}\\
y &=& -2\left(\frac{4}{5}\right) + 1 = -\frac{8}{5} + 1\\
y &=&-\frac{3}{5}
\end{eqnarray}\]
Maximum/Minimum values of a Quadratic
\(\frac{-b}{2a} = \cases{x_{(y_{max})}, & if a < 0\cr x_{(y_{min})}, & if a > 0\cr}\)
Multiple variables in a linear system
\(\begin{eqnarray} 2x & + y & + z &=& 5\cr 4x &- 6y & &=& -2\cr -2x &+ 7y & + 2z &=& 9 \cr \end{eqnarray}\)
\(\left[\begin{matrix} 2 & 1M& 1\cr 4&-6& 0\cr -2& 7& 2&\cr\end{matrix}\right] \left[ \begin{matrix} x \cr y \cr z \cr\end{matrix}\right] = \left[\begin{matrix} 5\cr -2\cr 9 \cr \end{matrix}\right]\)
Solution by matrix rearrangments (2)
- Gaussian elimination of first variable
\(\left[ \begin{matrix} 1 & \frac{1}{2} & \frac{1}{2}\cr 4-2\times2 &-6-2\times1 & 0-2\times1\cr -2+2& 7+1& 2+1\cr\end{matrix}\right] \left[ \begin{matrix} x \cr y \cr z \cr\end{matrix}\right] = \left[\begin{matrix} \frac{5}{2}\cr -2-2\times5\cr 9 + 5\cr \end{matrix}\right]\)
\(\left[ \begin{matrix} 1 & \frac{1}{2} & \frac{1}{2}\cr 0 &-8 & -2\cr 0& 8& 3\cr\end{matrix}\right] \left[ \begin{matrix} x \cr y \cr z \cr\end{matrix}\right] = \left[\begin{matrix} \frac{5}{2}\cr -12\cr 14\cr \end{matrix}\right]\)
Solution by matrix rearrangments (3)
- Gaussian elimination of second variable
\(\left[ \begin{matrix} 1 & \frac{1}{2} & \frac{1}{2}\cr 0 &\frac{-8}{-8} & \frac{-2}{-8}\cr 0& 8-8& 3-2\cr\end{matrix}\right] \left[ \begin{matrix} x \cr y \cr z \cr\end{matrix}\right] = \left[\begin{matrix} \frac{5}{2}\cr \frac{-12}{-8}\cr 14-12\cr \end{matrix}\right]\)
\(\left[ \begin{matrix} 1 & \frac{1}{2} & \frac{1}{2}\cr 0 & 1 & \frac{1}{4}\cr 0& 0& 1\cr\end{matrix}\right] \left[ \begin{matrix} x \cr y \cr z \cr\end{matrix}\right] = \left[\begin{matrix} \frac{5}{2}\cr \frac{3}{2}\cr 2\cr \end{matrix}\right]\)
Solution by matrix rearrangments (4)
\(\left[ \begin{matrix} 1 & \frac{1}{2} & 0 \cr 0 & 1 & 0 \cr 0& 0& 1\cr\end{matrix}\right] \left[ \begin{matrix} x \cr y \cr z \cr\end{matrix}\right] = \left[\begin{matrix} \frac{3}{2}\cr 1 \cr 2\cr \end{matrix}\right]\)
Solution by matrix rearrangments (5)
- Back substitution of 2nd variable
\(\left[ \begin{matrix} 1 & \frac{1}{2}-\frac{1}{2} & 0 \cr 0 & 1 & 0 \cr 0& 0& 1\cr\end{matrix}\right] \left[ \begin{matrix} x \cr y \cr z \cr\end{matrix}\right]= \left[\begin{matrix} \frac{3}{2} - \frac{1}{2} \cr 1 \cr 2\cr \end{matrix}\right]\)
\(\left[ \begin{matrix} 1 & 0 & 0 \cr 0 & 1 & 0 \cr 0& 0& 1\cr\end{matrix}\right] \left[ \begin{matrix} x \cr y \cr z \cr\end{matrix}\right] = \left[\begin{matrix} 1 \cr 1 \cr 2\cr \end{matrix}\right]\)
\(\left[ \begin{matrix} x \cr y \cr z \cr\end{matrix}\right] = \left[\begin{matrix} 1 \cr 1 \cr 2\cr \end{matrix}\right]\)
Solution by matrix rearrangments (6)
\[\left[\begin{matrix} 2 & 1 & 1\cr 4&-6& 0\cr -2& 7& 2&\cr\end{matrix}\right] \left[\begin{matrix} 1 \cr 1 \cr 2\cr \end{matrix}\right] = \left[\begin{matrix} 2\times 1 + 1\times 1 +1\times 2\cr 4 \times 1 + -6\times 1 + 0\times 2\cr -2\times 1+ 7\times 1 + 2\times 2 \cr\end{matrix}\right] =\]
\[\left[\begin{matrix} 2 + 1 + 2\cr 4 + -6 \cr -2 + 7 + 4\cr\end{matrix}\right] = \left[\begin{matrix} 5\cr -2\cr 9 \cr \end{matrix}\right]\]
Chemical Stoichiometry
\[C_6H_{12}O_6 + O_2 \longrightarrow CO_2 + H_2O\]
Setup the Stoichiometry Table
Number of Molecules |
\(x\) |
\(y\) |
\(z\) |
\(w\) |
Sugar molecule |
\(x = 1\) |
|
|
|
Carbon atoms |
\(6x\) |
|
\(-z\) |
|
Hydrogen atoms |
\(12x\) |
|
|
\(-2w\) |
Oxygen atoms |
\(6x\) |
\(2y\) |
\(-2z\) |
\(-w\) |
Matrix version
\[\left[\begin{matrix} 1 & 0 & 0 & 0\cr 6 & 2 & -2 & -1\cr12 & 0 & 0 & -2\cr 6 & 0 & -2 & 0 \cr\end{matrix}\right]\left[\begin{matrix}x\cr y\cr z\cr w\cr\end{matrix}\right] = \left[\begin{matrix}1\cr0\cr0\cr0\cr\end{matrix}\right]\]
- Gaussian elimination of the first variable
\[\left[\begin{matrix} 1 & 0 & 0 & 0\cr 0 & 2 & -2 & -1\cr 0 & 0 & 0 & -2\cr 0 & 0 & -2 & 0 \cr\end{matrix}\right]\left[\begin{matrix}x\cr y\cr z\cr w\cr\end{matrix}\right] = \left[\begin{matrix}1\cr -6\cr -12\cr -6\cr\end{matrix}\right]\]
Stoichiometry
- Gaussian elimination of the second variable
\[\left[\begin{matrix} 1 & 0 & 0 & 0\cr 0 & 1 & -1 & -\frac{1}{2}\cr 0 & 0 & 0 & -2\cr 0 & 0 & -2 & 0 \cr\end{matrix}\right]\left[\begin{matrix}x\cr y\cr z\cr w\cr\end{matrix}\right] = \left[\begin{matrix}1\cr -3\cr -12\cr -6\cr\end{matrix}\right]\]
- Gaussian elimination of the 3rd and 4th variable
\[\left[\begin{matrix} 1 & 0 & 0 & 0\cr 0 & 1 & -1 & -\frac{1}{2}\cr0 & 0 & 1 & 0 \cr 0 & 0 & 0 & 1\cr \end{matrix}\right]\left[\begin{matrix}x\cr y\cr z\cr w\cr\end{matrix}\right] = \left[\begin{matrix}1\cr -3\cr 3\cr 6\cr\end{matrix}\right]\]
Stoichiometry
\[\left[\begin{matrix} 1 & 0 & 0 & 0\cr 0 & 1 & 0 & 0 \cr0 & 0 & 1 & 0 \cr 0 & 0 & 0 & 1\cr \end{matrix}\right]\left[\begin{matrix}x\cr y\cr z\cr w\cr\end{matrix}\right] = \left[\begin{matrix}1\cr 3\cr 3\cr 6\cr\end{matrix}\right]\]
\[C_6H_{12}O_6 + 3 O_2 \longrightarrow 3 CO_2 + 6 H_2O\]
Stoichiometry
\[\left[\begin{matrix} 1 & 0 & 0 & 0\cr 6 & 2 & -2 & -1\cr12 & 0 & 0 & -2\cr 6 & 0 & -2 & 0 \cr\end{matrix}\right]\left[\begin{matrix}1\cr 3\cr 3\cr 6\cr\end{matrix}\right] = \left[\begin{matrix}1\cr6+6-6-6\cr12-12\cr6-6\cr\end{matrix}\right]=\left[\begin{matrix}1\cr0\cr0\cr0\cr\end{matrix}\right]\]
Exercise:
\[IO_3^- + I^- + H^+ \longrightarrow I_3^- + H_2O\]
Molecules |
\(IO_3^-\) |
\(I^-\) |
\(H^+\) |
\({I_3}^-\) |
\(H_2O\) |
- |
I |
\(x\) |
\(y\) |
|
\(-3w\) |
|
0 |
O |
\(3x\) |
|
|
|
\(-v\) |
0 |
H |
|
|
\(z\) |
|
\(-2v\) |
0 |
electrons |
\(x\) |
\(y\) |
\(-z\) |
\(-w\) |
|
0 |
Multiple |
\(x\) |
|
|
|
|
1 |
\[IO_3^- + 8I^- + 6H^+ \longrightarrow 3{I_3}^- + 3H_2O\]