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# Expressions and Equations

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Expressions and Equations
ALGEBRA Expressions and Equations

Creating expressions Note: × and ÷ are not often used in Algebra
i.e. 5 × x = 5x i.e. 8 ÷ x = 8 x Also a dot ‘.’ means multiply i.e. 2x . 2y = 2x × 2y Creating expressions - Using suitable symbols to express rules e.g. Write an expression for each of the following Let n = a number a) A number with 12 added to it n + 12 b) A number with 9 subtracted from it n - 9 c) A number multiplied by 2 n × 2 Best written as 2n d) A number divided by 6 n ÷ 6 Best written as n 6 As long as you explain what a symbol represents, any symbol can be used

e.g. John has x dollars. How much will he have if:
a) He spends \$35 x - 35 50 - 35 = \$15 x + 28 50 + 28 = \$78 b) He is given \$28 c) He doubles his money 2 x 2 x 50 = \$100 d) He spends half x 50 = \$25 2 2 Once you have an expression, it can be used to calculate values if you know what the ‘variable’ (symbol) is worth. e.g. John has \$50, use the expressions to calculate how much he will have in each situation:

Simplifying expressions by multiplying
- ALL terms can be multiplied Rules: 1) Multiply all numbers in the expression 2) Place letters in alphabetical order behind product e.g. Simplify: a) p × 2q = 1 × 2 × p × q b) 2a × 5b = 2 × 5 × a × b = 2pq = 10ab c) 3 × 4x × 2y = 3 × 4 × 2 × x × y No number = 1 i.e. p = 1p = 24xy LIKE and UNLIKE TERms - LIKE terms are those with exactly the same letter or combination of letters LIKE terms: 2x, 3x, 31x UNLIKE terms: 2x, 3 4ab, 7ab 5p, 6q 2ab, 2ac e.g. Circle the LIKE terms in the following groups: a) 3a 5b 6a 2c b) 2xy 4x xy 3z yx While letters should be in order, terms are still LIKE if they are not.

Simplifying by adding/subtracting
- We ALWAYS aim to simplify expressions from expanded to compact form - Only LIKE terms can be added or subtracted - When adding/subtracting just deal with the numbers in front of the letters e.g. Simplify these expanded expressions into compact form: a) a + a + a = ( )a b) 5x + 6x + 2x = ( )x = 3a = 13x c) 3p + 7q + 2p + 5q = (3 + 2)p ( )q d) 4a + 3b + 7a + b 1 = 5p + 12q = (4 + 7)a ( )b = 11a + 4b - For expressions involving both addition and subtraction take note of signs e.g. Simplify the following expressions: a) 4x + 2y – 3x = (4 – 3)x + 2y b) 3a – 4b – 6a + 9b = x + 2y = (3 - 6)a ( )b = -3a + 5b c) -5d + 4a d - 5a = ( )a ( )d + 2 = -a + q + 2 If the number left in front of a letter is 1, it can be left out d) 2a – 5b – 6c = 2a – 5b – 6c

SUBSTITUTION - Involves replacing variables with numbers and calculating the answer - Remember the BEDMAS rules e.g. If a = 7, b = 3, and c = 5, calculate the following a) a + b + c = b) b - a = 3 - 7 = 15 = -4 c) abc = 7 × 3 × 5 = 105 - Or replacing numbers into formulas e.g. The area of a triangle is given by the formula A = ½b × h Find the area of: Area = ½ × 12 × 5 5 m = 30 m2 12 m - Can substitute using mixed operations e.g. If a = 2, and b = 5, calculate the following a) 5b – 4a = 5 × 5 – 4 × 2 b) ab + 15 = 2 × = = = 17 = 25

Because the top needs to be calculated first, brackets are implied
- But always calculate brackets first! e.g. If a = 2, and b = 5, calculate the following a) 4(a + b) = 4(2 + 5) b) 2b – a 4 = (2 × 5 – 2) 4 = 4 × 7 = (10 – 2) 4 = 28 = 8 4 = 2 - Can involve powers too which are done after brackets e.g. If a = 2, and b = 5, calculate the following a) a2 = 22 b) (b – 2)2 = (5 – 2)2 = 4 = 32 = 9 c) 4a2 = 4 × 22 d) 2b2 – 3a2 = 2 × × 22 = 4 × 4 = 2 × × 4 = 16 = = 38

POwers - Remember: 3 × 3 × 3 × 3 = 34
- Variables (letters) that are multiplied by themselves are treated the same way e.g. Simplify these expressions that are written in full a) r × r = r2 b) p × p × p × p × p = p5 - Sometimes there may be two or more variables e.g. Simplify a) a × a × b × b × b = a2b3 b) d × e × e × d × f = d2e2f Letters should still be written in alphabetical order! - With numbers and variables, multiply numbers and combine variables e.g. Simplify a) 4x × 6x = 4 × 6 × x × x b) 6b × 3b × 2 = 6 × 3 × 2 × b × b = 24x2 = 36b2 c) 2a × 5b × 3a × b 1 = 2 × 5 × 3 × 1 × a × a × b × b = 30a2b2

Multiplying using POwers
- Does x2 × x3 = x × x × x × x × x ? YES - Therefore x2 × x3 = x5 - How do you get = 5 ? + - When multiplying index (power) expressions with the same letter, ADD the powers. No number = 1 i.e. p = 1p1 e.g. Simplify a) p10 × p2 = p(10 + 2) b) a3 × a2 × a = a( ) 1 = p12 = a6 - Remember to multiply any numbers in front of the variables first e.g. Simplify a) 2x3 × 3x4 = 2 × 3 x(3 + 4) b) 2a2 × 3a × 5a4 1 = 6 x7 = 2 × 3 × 5 a( ) = 30 a7

dividing using POwers - Does 6 = 1 ? 6 YES - Therefore x = 1 x
- Does x5 = x × x × x × x × x ? x x × x × x YES = x × x × 1 × 1 × 1 - Therefore x5 = x2 x3 - How do you get = 2 ? - - When dividing index (power) expressions with the same letter, SUBTRACT the powers. e.g. Simplify a) p5 ÷ p = p(5 - 1) b) x7 x4 = x(7 - 4) 1 = p4 = x3 - Remember to divide any numbers in front of the variables first e.g. Simplify a) 12x5 ÷ 6x4 = 12 ÷ 6 x(5 - 4) b) a7 15a2 ÷ 5 = 1 5 a(7 - 2) = 2 x = 1 5 a5 or a5 5 If the power remaining is 1, it can be left out

Expanding expressions
- Does 6 × (3 + 5) = 6 × × 5 ? YES 6 × 8 = 48 = 48 - The removal of the brackets is known as the distributive law and can also be applied to algebraic expressions - When expanding, simply multiply each term inside the bracket by the term directly in front e.g. Expand a) 6(x + y) = 6 × x + 6 × y b) -4(x – y) = -4 × x - -4 × y = 6x + 6y = -4x + 4y c) -4(x – 6) = -4 × x - -4 × 6 d) 7(3x – 2) = 7 × 3x - 7 × 2 = -4x + 24 = 21x - 14 e) x(2x + 3y) = x × 2x + x × 3y f) -3x(2x – 5) = -3x × 2x - -3x × 5 = 2x2 + 3xy = -6x2 + 15x Don’t forget to watch for sign changes!

- If there is more than one set of brackets, expand them all then collect any like terms.
e.g. Expand and simplify a) 2(4x + y) + 8(3x – 2y) = 2 × 4x + 2 × y + 8 × 3x - 8 × 2y = 8x + 2y + 24x - 16y = 32x - 14y b) -3(2a – 3b) – 4(5a + b) = -3 × 2a - -3 × 3b - 4 × 5a + -4 × 1b = -6a + 9b - 20a - 4b = -26a + 5b

factorising expressions
- Factorising is the reverse of expanding - To factorise: 1) Look for a common factor to put outside the brackets 2) Inside brackets place numbers/letters needed to make up original terms You should always check your answer by expanding it e.g. Factorise a) 2x + 2y = 2( ) x + y b) 2a + 4b – 6c = 2( ) a + 2b - 6c - Always look for the highest common factor e.g. Factorise a) 6x - 15 = 3( ) 2x - 5 b) 30a + 20 = 10( ) 3a + 2 - Sometimes a ‘1’ will need to be left in the brackets e.g. Factorise a) 6x + 3 = 3( ) 2x + 1 b) 20b - 10 = 10( ) 2b - 1

- Letters can also be common factors
e.g. Factorise a) cd - ce = c( ) d - e b) xyz + 2xy – 3yz = y( ) xz + 2x - 3z c) 4ad – 8a = 4 ( ) a d - 2 - Powers greater than 1 can also be common factors e.g. Factorise a) 5a2 – 7a5 = a2( ) 5 - 7a3 b) 4b2 + 6b3 = 2b2( ) 2 + 3b

SOLVING EQUATIONS - When solving we need to isolate the unknown variable to find its value - To isolate we work backwards by undoing operations 1) To undo multiplication we use division e.g. Solve 3x = 18 ÷3 ÷3 x = 6 2) To undo addition we use subtraction e.g. Solve x + 2 = 6 -2 -2 x = 4 3) To undo subtraction we use addition e.g. Solve x - 8 = 11 +8 +8 x = 19 4) To undo division we use multiplication e.g. Solve x = 6 5 ×5 ×5 x = 30

Don’t forget the integer rules!
- Terms containing the variable (x) should be placed on one side (often left) e.g. Solve a) 5x = 3x + 6 b) -6x = -2x + 12 -3x -3x +2x +2x 2x = 6 -4x = 12 Don’t forget the integer rules! ÷2 ÷2 ÷-4 ÷-4 x = 3 x = -3 Always line up equals signs and each line should contain the variable and one equals sign You should always check your answer by substituting into original equation Always look at the sign in front of the term/number to decide operation - Does 5×3 = 3×3 + 6 ? YES - Does -6×-3 = -2× ? YES 15 = 9 + 6 18 = - Numbers should be placed on the side opposite to the variables (often right) e.g. Solve a) 6x – 5 = 13 b) -3x + 10 = 31 +5 +5 -10 -10 6x = 18 -3x = 21 ÷6 ÷6 ÷-3 ÷-3 x = 3 x = -7

- Same rules apply for combined equations
e.g. Solve a) 5x + 8 = 2x + 20 b) 4x - 12 = -2x + 24 -2x -2x +2x +2x 3x + 8 = 20 6x - 12 = 24 -8 -8 +12 +12 3x = 12 6x = 36 ÷3 ÷3 ÷6 ÷6 x = 4 x = 6 - Answers can also be negatives and/or fractions e.g. Solve a) 8x + 3 = -12x - 17 b) 5x + 2 = 3x + 1 +12x +12x -3x -3x 20x + 3 = -17 2x + 2 = 1 -3 -3 -2 -2 20x = -20 2x = -1 ÷20 ÷20 ÷2 ÷2 x = -1 x = -1 2 Make sure you don’t forget to leave the sign too! Answer can be written as a decimal but easiest to leave as a fraction

- Expand any brackets first
e.g. Solve a) 3(x + 1) = 6 b) 2(3x – 1) = x + 8 3x + 3 = 6 6x - 2 = x + 8 -3 -3 -x -x 3x = 3 5x - 2 = 8 ÷3 ÷3 +2 +2 x = 1 5x = 10 ÷5 ÷5 x = 2

Writing EQUATIONS and solving
- Involves writing an equation and then solving e.g. Write an equation for the following information a) I think of a number, multiply it by 3 and then add 12. The result is 36. Let n = a number 3 n + 12 = 36 a) I think of a number, multiply it by 5 and then subtract 4. The result is the same as if 18 were added to the number Let n = a number 5 n - 4 = n + 18 e.g. Write an equation for the following information and solve a) A rectangular pool has a length 5m longer than its width. The perimeter of the pool is 58m. Find its width x + 5 x x + x x = 58 4x + 10 = 58 Draw a diagram -10 -10 x x 4x = 48 Let x = width ÷4 ÷4 x + 5 x = 12 Therefore width is 12 m

b) I think of a number and multiply it by 7
b) I think of a number and multiply it by 7. The result is the same as if I multiply this number by 4 and add 15. What is this number? Let n = a number 7 n = n 4 + 15 -4n -4n 3n = 15 ÷3 ÷3 n = 5 Therefore the number is 5

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