Algebra, functions, equations and data in explicit models
Algebraic Operations
What this domain tests
The Algebraic operations domain tests whether you can rewrite expressions accurately and recognize structure before calculating. The subject methods include polynomial arithmetic, factoring, rational expressions, exponent laws, radicals, and complex numbers. Most errors come from illegal cancellation or from ignoring restrictions on variables.
Polynomials and factoring
- Add and subtract by combining like terms; multiply each term of one polynomial by each term of the other. For nonzero polynomials over the real numbers, the degree of their product is the sum of their degrees.
- Memorize special products: $(a\pm b)^2=a^2\pm 2 ab+b^2$, $(a+b)(a-b)=a^2-b^2$, and $a^3\pm b^3=(a\pm b)(a^2\mp ab+b^2)$.
- Factoring strategy: greatest common factor first, then grouping, difference of squares, sum or difference of cubes, or trinomial trial. State the coefficient domain: a factorization over integers need not be complete over the real or complex numbers.
Rational expressions and exponents
- Cancel factors, never terms: $\frac{x+2}{2}$ cannot become $x+1$.
- For $x^{m/n}$, take the $n$th root and raise to the $m$; negative exponents move the factor across the fraction bar.
- State excluded values where a denominator is zero before simplifying. Simplifying does not restore them.
Radicals and complex numbers
- Simplify radicals by extracting perfect-power factors; rationalize denominators using conjugates.
- Since $i^2=-1$, add and subtract complex numbers componentwise, multiply as binomials and replace $i^2$, and divide by multiplying numerator and denominator by the conjugate.
Worked example
Simplify $\frac{x^2-4}{x^2-x-6}\cdot\frac{x^2-9}{x+2}$ and list restrictions.
Factor: $\frac{(x-2)(x+2)}{(x-3)(x+2)}\cdot\frac{(x-3)(x+3)}{x+2}$. Before canceling, note $x\ne 3$ and $x\ne-2$. Canceling $(x+2)$ and $(x-3)$ leaves $\frac{(x-2)(x+3)}{x+2}$, with $x\ne 3,-2$. Check $x=0$: the original equals $\left(\frac{-4}{-6}\right)\left(\frac{-9}{2}\right)=-3$, and the simplified expression equals $\frac{(-2)(3)}{2}=-3$.
Traps that cost marks
- Writing $(a+b)^2=a^2+b^2$ and omitting the middle term $2 ab$.
- Canceling a term shared by numerator and denominator rather than a common factor.
- Forgetting that a simplified rational expression keeps the original domain restrictions.
- Applying a negative exponent only to the coefficient, as in treating $(2 x)^{-2}$ as $2 x^{-2}$.
Equations and Inequalities
What this domain tests
The Equations and inequalities domain tests solving and interpreting solution sets: linear and quadratic equations, rational and radical equations, absolute value, systems, and inequalities. These exercises combine both algebraic solutions and correct interval notation, including excluded values.
Linear equations and systems
- Solve linear equations by applying inverse operations to both sides. An identity is true for all values; a contradiction has no solution.
- For systems, substitution or elimination gives an ordered pair. Parallel distinct lines produce no solution; the same line produces infinitely many solutions. Always check the ordered pair in both original equations.
Quadratic equations
- Write in standard form $ax^2+bx+c=0$. Use factoring and the zero product property, the square root property, completing the square, or the quadratic formula.
- The discriminant $b^2-4 ac$ determines the type of roots: positive gives two distinct real roots, zero gives one repeated real root, and negative gives two complex conjugate roots.
- For $ax^2+bx+c=0$, the sum of roots is $-b/a$ and the product is $c/a$.
Inequalities and absolute value
- Multiplying or dividing an inequality by a negative number reverses its direction.
- For $k>0$, $|X|<k$ means write $-k<X<k$; and for $k>0$, $|X|>k$ means write $X<-k$ or $X>k$.
- For rational inequalities, find critical values from numerator and denominator, test intervals on a sign chart, and exclude zeros of the denominator. Use a bracket at a numerator zero only if the inequality allows equality and the expression is defined there.
Radical and rational equations
- Squaring both sides can introduce extraneous solutions, so every candidate must be checked in the original equation.
Worked example
Solve $\sqrt{2 x+3}=x$.
Square both sides: $2 x+3=x^2$, so $x^2-2 x-3=0$, which factors as $(x-3)(x+1)=0$. Candidates are $x=3$ and $x=-1$. Check $x=3$: $\sqrt{9}=3$, valid. Check $x=-1$: $\sqrt{1}=1$, but the right side is $-1$, so it is extraneous. The solution set is ${3}$. Squaring erased the sign information that the check restores.
Traps that cost marks
- Forgetting to reverse an inequality after multiplying or dividing by a negative.
- Using a closed interval at a value that makes a denominator zero.
- Dividing both sides by a variable and losing the solution where that variable equals zero.
- Skipping the check after squaring a radical equation.
Functions and Their Properties
What this domain tests
The Functions and their properties domain tests the function concept across algebraic and graphical representations: notation, domain and range, composition, inverses, transformations, and basic behavior of parent functions. Useful practice includes questions that combine two ideas, such as finding the domain of a composition.
Domain and range
- The domain is the set of allowed inputs. Exclude values that make a denominator zero and, for even roots, values that make the radicand negative.
- The range is the set of outputs. Use the graph, vertex, asymptotes, or end behavior to determine it.
- Express domains and ranges in interval notation, using parentheses at excluded values and infinities.
Composition and inverses
- $(f\circ g)(x)=f(g(x))$. Its domain requires $x$ in the domain of $g$ and $g(x)$ in the domain of $f$.
- An inverse exists only for a one-to-one function; the horizontal line test detects whether each output has a unique input.
- To find an inverse, swap $x$ and $y$ and solve for $y$. The domain and range of $f$ and $f^{-1}$ interchange, and $f(f^{-1}(x))=x$ on the appropriate domain.
Transformations and parent graphs
- $y=f(x-h)+k$ shifts the graph $h$ units right and $k$ units up.
- $y=af(x)$ stretches vertically when $|a|>1$ and compresses when $0<|a|<1$; negative $a$ reflects across the $x$-axis.
- $y=f(-x)$ reflects across the $y$-axis. Apply transformations in a consistent order, handling horizontal shifts and scalings inside the argument carefully.
Worked example
Find the inverse of $f(x)=\frac{2 x+1}{x-3}$.
Write $y=\frac{2 x+1}{x-3}$ and swap: $x=\frac{2 y+1}{y-3}$. Multiply: $x(y-3)=2 y+1$, so $xy-3 x=2 y+1$. Collect $y$ terms: $xy-2 y=3 x+1$, hence $y(x-2)=3 x+1$ and $y=\frac{3 x+1}{x-2}$. Thus $f^{-1}(x)=\frac{3 x+1}{x-2}$, with $x\ne 2$. The original function excludes $x=3$ from its domain, and its inverse excludes $x=2$ from its domain, matching the range restriction.
Traps that cost marks
- Assuming $f(g(x))=g(f(x))$; composition is generally not commutative.
- Ignoring the inner function's domain when finding the domain of a composition.
- Reading $f^{-1}(x)$ as $1/f(x)$ rather than as inverse notation.
- Confusing horizontal and vertical line tests, or shifting a graph in the wrong direction.
Algebra, functions and data in stated models
Translate a numerical story into a model before manipulating symbols. Identify the variable and its unit, the fixed quantities, and any restrictions such as whole-number counts or nonnegative time. A fixed joining fee plus a monthly charge has the formC=b+mx. The intercept represents the initial charge and the slope the change per additional month in that stated model. A line may fit a classroom example without describing every real membership contract or every future observation.
For an inequality, interpret the boundary phrase carefully. At least includes the threshold and gives a greater-than-or-equal relation; at most includes it with a less-than-or-equal relation. Check a candidate in the original story after solving. A negative number of tickets may solve an algebraic equation but fail the count restriction. For two equations, a common solution must satisfy both; parallel distinct lines do not share a point, while two forms of the same line describe one common set.
Functions assign each permitted input exactly one output. Their tables, graphs, formulas and verbal descriptions emphasize different properties. Distinguish an input restriction from an output range, an intercept from a rate of change, and a zero from a point where the function is undefined. In a quadratic model, identify what the vertex represents and whether it lies in the allowed domain. A mathematical vertex outside a supplied time interval need not be an attainable physical maximum.
Data questions add another layer of interpretation. Compute the mean from sum divided by count; use the ordered middle observation or pair for the median. An extreme observation can affect the mean differently from the median. Compare a spread measure when two groups have the same center, and check whether a graph changes its scale or begins above zero. A scatterplot association can suggest a pattern without proving that one variable causes the other. The sample, method and possible confounding variables matter.
For example, a fee modelC=40+25 m with budget 215 gives 40+25 m<=215, hence m<=7. If months must be nonnegative whole numbers, the permitted counts are 0 through 7. The original inequality and 25 m<=175 describe the same feasible set; a question claiming they are different answers would be defective. This check illustrates why equivalent algebraic forms and units must be evaluated before accepting a proposed multiple-choice key.