Algebra Flashcards Preview

GRE 2017 > Algebra > Flashcards

Flashcards in Algebra Deck (19):
1

Expression

Does not have an = sign

2

Denominator trick

If your equation contains a denominator,
- Put parentheses around the ENTIRE equation, and
- MULTIPLY it by the denominator

If the equation contains MULTIPLE DENOMINATORS
- Eliminate them by multiplying by the lowest common denominator (LCD)

3

When to cross-multiply?

If one fraction equals another

(x+1)/3 = (2x-5)/4

4

When working with inequalities, beware of...

Multiplying or dividing by a variable (you may need to flip the sign!)

Must consider BOTH scenarios (negative variable, positive variable)

5

Compound inequalities - how to isolate the variable in the middle?

Do the same thing to all 3 sides

6

How to solve an equation with variables AND numbers inside the absolute value brackets?

1. Isolate the absolute value brackets
2. Drop the brackets, and place +/- sign in front of the algebra (NOT in front of the answer)
3. You will then get 2 equations (2 possible answers) - solve for both of them
BUT BEWARE THAT BOTH ARE NOT ALWAYS VALID

7

Elimination strategy when solving 2 equations (with >1 variable)

1. Stack the equations atop one another
2. Arrange the variables in the same order
3. Add or subtract equations to ELIMINATE one of the variables

If necessary, MULTIPLY one (or both) of the equations by some value to give either variable opposite coefficients

8

Equations with even exponents...

...Have 2 solutions

(x-3)^2 = 25
Then,
x-3=5 and x-3=-5

9

Taking the root of an even exponent

Results in an absolute value

10

Quadratic functions - how to solve?

x^2 + 3x + 1

1. Set equal to 0
2. Make sure the x^2 term is positive
3. Factor

(x ) (x )

Numbers should MULTIPLY to the LAST value, and ADD to the MIDDLE value

11

Quadratic functions - what is a solution?

Same as the "root" - the answer to both of the factors

12

Factors of a quadratic equation?

Set each factor to 0 and solve.

X^2 + 7X + 10 =0 --> (X+2)(X+5) these are the "factors"

X+2=0 and X+5=0

X=-2 and X=-5 these are the "roots" aka "solutions"

13

(x + 2)(x + 3) = 0

How to solve for x?

DO NOT FOIL! This quadratic has already been factored. Set each factor = 0 and solve for the "roots" or "solutions."

14

(x + y)^2

x^2 + 2xy + y^2

X squared + 2xy + y squared

15

(x - y)^2

x^2 - 2xy + y^2

16

(x + y) (x - y)

x^2 - y^2

17

Plug in question

The comparison of expressions (variables can have limitless or nearly limitless values)

Goal is to prove an inconsistent relationship between the 2 quantities

Always test at least 3 values (generally -1, 0 and 1 if possible)

Remove any items shared by the two expressions

18

Manipulating algebra for a "plug-in" question

1. Add or subtract anything you want from both sides
2. Multiply or divide both sides by a POSITIVE value
3. Square or square root both quantities - IF they are positive

19

To solve an equation with TWO denominators

Multiply the ENTIRE equation by the LCD