Mathematics
Grade 10
15 min
Solve a quadratic equation by completing the square
Solve a quadratic equation by completing the square
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1
Introduction & Learning Objectives
Learning Objectives
Identify the 'b' coefficient in a quadratic equation and calculate the value needed to create a perfect square trinomial.
Transform a quadratic expression of the form x² + bx into a perfect square trinomial.
Solve quadratic equations where the leading coefficient 'a' is 1 by completing the square.
Solve quadratic equations where the leading coefficient 'a' is not 1 by completing the square.
Apply the square root property correctly to find all possible real solutions.
Explain the steps required to isolate the variable after creating a perfect square.
Ever tried to fit a puzzle piece that's almost right? 🤔 Completing the square is like finding the exact missing piece to turn a complicated quadratic into a simple, perfect...
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Key Concepts & Vocabulary
TermDefinitionExample
Quadratic Equation (Standard Form)An equation that can be written in the form ax² + bx + c = 0, where a, b, and c are constants and a ≠ 0.2x² - 5x + 3 = 0 is a quadratic equation where a=2, b=-5, and c=3.
Perfect Square TrinomialA trinomial (an expression with three terms) that is the result of squaring a binomial. It can be factored into (x + k)² or (x - k)².x² + 10x + 25 is a perfect square trinomial because it can be factored as (x + 5)².
CoefficientA number used to multiply a variable. In this topic, we are most interested in the 'b' coefficient, the number multiplying the x term.In the expression x² - 6x + 9, the coefficient 'b' is -6.
Constant TermA term in an algebraic expression that does not contain any variables; its value is fixed.In ax...
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Core Formulas
The 'Completing the Square' Value
c = (b/2)²
To turn an expression like x² + bx into a perfect square trinomial, you must add a specific constant 'c'. This constant is found by taking the 'b' coefficient, dividing it by 2, and then squaring the result.
Factoring a Perfect Square Trinomial
x² + bx + (b/2)² = (x + b/2)²
Once you have added the value (b/2)² to complete the square, the resulting trinomial can always be factored into a binomial squared. The term inside the parentheses is always 'x' plus half of the original 'b' coefficient.
The Square Root Property Formula
If X² = d, then X = ±√d
This is the final step in solving. After you have an equation in the form (x + k)² = d, you take the square root of both sides....
4 more steps in this tutorial
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Challenging
The equation x² + bx - 10 = 0 is solved by completing the square, and one of the solutions is x = 2. What is the value of the coefficient 'b'?
A.3
B.-3
C.8
D.5
Easy
What value must be added to the expression x² + 10x to create a perfect square trinomial?
A.5
B.100
C.25
D.10
Easy
According to the tutorial, what is the general formula to find the constant term 'c' that creates a perfect square trinomial from an expression of the form x² + bx?
A.c = (b/2)²
B.c = b/2
C.c = b²
D.c = 2b
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