Mathematics Grade 9 15 min

Subtract zero/all

Subtract zero/all

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1

Introduction & Learning Objectives

Learning Objectives Identify and apply the Identity Property of Subtraction (subtracting zero) to simplify variable expressions. Apply the principle of subtracting an expression from itself (subtracting all) to simplify polynomials and functions. Use the 'subtract all' concept to create zero pairs when isolating variables in multi-step linear and quadratic equations. Correctly distribute a negative sign when subtracting an entire polynomial expression. Differentiate between an operation that results in zero (e.g., x - x = 0) and an operation that leaves a variable unchanged (e.g., x - 0 = x). Analyze and solve equations where terms on both sides cancel out, leading to a simplified equation. If you have a polynomial `P(x)` and you take away nothing, what's left...
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Key Concepts & Vocabulary

TermDefinitionExample Identity Property of SubtractionA property stating that when zero is subtracted from any number or expression, the result is the original number or expression.For the polynomial `p(x) = 3x^2 + 5`, `p(x) - 0 = 3x^2 + 5`. Zero PairA pair of terms that are additive inverses, meaning they add up to zero. In subtraction, this occurs when a term is subtracted from itself.In the expression `7x - 7x`, the terms `7x` and `-7x` form a zero pair, and the result is `0`. Subtracting AllThe action of subtracting an entire quantity, expression, or variable from an identical one, always resulting in zero.`(4x - 9) - (4x - 9) = 0`. Isolating a VariableThe process of rearranging an equation to get a specific variable by itself on one side of the equals sign. This often involves creati...
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Core Formulas

Identity Property of Subtraction For any algebraic expression A, A - 0 = A Use this rule when simplifying expressions where zero is being subtracted. It confirms that the expression remains unchanged. The 'Subtract All' Principle For any algebraic expression A, A - A = 0 This is the fundamental rule used to eliminate terms when solving equations. By subtracting a term from both sides of an equation, you effectively use this principle to remove it from one side.

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Sample Practice Questions

Challenging
Let f(x) = 3x² + 5x - 1 and g(x) = x² + 5x + 4. Solve the equation f(x) - g(x) = 12.
A.x = 4 and x = -4
B.x = 3 and x = -3
C.x = 2 and x = -2
D.x = 1 and x = -1
Challenging
For the equation (k-3)x² + 2x = (2k-9)x² + 2x - 15, for what value of k do the quadratic terms form a zero pair, simplifying the equation?
A.k = 3
B.k = 6
C.k = -6
D.k = 4.5
Challenging
Consider the equation (7x + c) - (ax - 5) = 0. For this equation to be true for all values of x (i.e., have infinite solutions), what must be the values of a and c?
A.a = 7, c = 5
B.a = -7, c = -5
C.a = 7, c = -5
D.a = -7, c = 5

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