Algebra, Geometry and Other Math: Algebra, Patterns and Logic
Variables, equations, inequalities, exponents cancelling factor by factor, patterns, sequences, and the logic and flowcharts E3n names in its own subscore.
11 topics · 50 questions
Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.
What a Variable Stands For
- How it worksHow does a box with a question mark in it turn into the letter x with nothing else changing?
- How it worksHow do 3x, x + 3 and x divided by 3 do three completely different things to the same number?
- Worked exampleFind the value of 4n - 7 when n is 5, and again when n is negative 2.
Writing Expressions from Words
- How it worksHow does each phrase in a sentence become one piece of an algebraic expression?
- Worked exampleFind the expression for the cost of b books at 7 dollars each plus a 4 dollar shipping fee.
- Worked exampleFind the expression for a number doubled, then increased by 5, then cut in half.
- Common mistakeWhy isn't twice the sum of x and 4 written as 2x + 4?
- Going furtherWhat happens to an expression when a second unknown joins in, like c cats and d dogs?
Solving Equations Step by Step
- How it worksHow does doing the same thing to both sides keep the scale balanced while x gets alone?
- How it worksHow do you undo operations in reverse order to peel a variable free?
- Worked exampleWalk me through solving 5x + 8 = 33 for x.
- Worked exampleWalk me through solving 3(x - 2) = x + 10 for x.
- Going furtherWhat happens when you solve an equation and end up with 5 = 5, or with 3 = 7?
Inequalities and the Flip
- How it worksHow does an inequality answer become a whole ray of the number line instead of one point?
- Worked exampleFind every x that makes 2x + 3 less than 11, and draw the answer on a number line.
- Worked exampleFind the solution to negative 3x greater than 12 and show exactly where the sign flips.
- Common mistakeWhy isn't an inequality solved the same way as an equation all the way through?
Properties of Exponents
- How it worksHow does writing out the repeated factors show why exponents add when powers multiply?
- How it worksHow do repeated factors cancel top against bottom when you divide two powers of the same base?
- Common mistakeWhy isn't anything raised to the zero power equal to zero?
- Worked exampleFind 34 divided by 32 by cancelling the repeated factors one at a time.
- Worked exampleFind the value of (23)2 and show why the two exponents multiply.
Algebraic Word Problems
- How it worksHow does one English sentence turn into one equation, phrase by phrase?
- How it worksHow do you set up a problem where two quantities are each described using the other?
- Worked exampleFind the two numbers that add to 40 when one of them is three times the other.
- Worked exampleFind Maya's age when she is 4 years older than her brother and their ages total 26.
- Common mistakeWhy isn't the answer to an algebra word problem always the value of x you just solved for?
Equations of Lines as Input-Output Rules
- How it worksHow does an equation of a line turn every input you feed it into exactly one output?
- Worked exampleFind y when x is 7 in the rule y = 4x - 5, then find x when y is 15.
- Worked exampleFind the rule that turns the inputs 1, 2 and 3 into the outputs 5, 8 and 11.
- Going furtherWhat tells you a rule draws a straight line rather than something that bends?
- Common mistakeWhy doesn't a table of x and y pairs have to come from a straight-line rule at all?
Patterns and the Rule Behind Them
- How it worksHow do you test a guessed rule against every term instead of only the first two?
- Worked exampleFind the next two terms of 1, 4, 9, 16, 25 and name the rule that makes them.
- Common mistakeWhy doesn't a pattern that opens 2, 4, 6 have to keep adding 2 forever?
Arithmetic and Geometric Sequences
- How it worksHow does each term of a sequence get built out of the term standing right before it?
- Worked exampleFind the 8th term of the sequence 4, 7, 10, 13 and show the shortcut that skips the rest.
- Worked exampleFind the 6th term of the sequence 2, 6, 18, 54.
- Common mistakeWhy isn't every sequence either an adding one or a multiplying one?
- Going furtherWhat changes about a sequence when the amount being added each time is negative?
Series and Repeating Cycles
- How it worksHow does pairing the first and last terms of an evenly spaced list make every pair total the same?
- How it worksHow does a repeating cycle let you predict the 100th item using only a remainder?
- Worked exampleFind the sum of 1 + 2 + 3 all the way up to 50 by pairing the ends.
- Worked exampleFind the 47th letter in the endlessly repeating pattern A, B, C, D.
- Going furtherWhat changes in the pairing trick when the list holds an odd number of terms?
Logic and Flowcharts
- How it worksHow does a flowchart send a number down a different branch depending on a yes or no test?
- How it worksHow do overlapping circles show which statements must be true and which only might be?
- Common mistakeWhy doesn't if it rains the game is cancelled mean a cancelled game proves it rained?
- Worked exampleWalk me through a machine that doubles 14 and then subtracts 3 whenever the result passes 20.
- Worked exampleFind the output when 7 enters a chart that triples it and then adds 1 if the result is odd.
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