Math Problem Statement

Solve this gcse question

Given that x^2 - 6x + 1 = (x - a)^2 - b for all values of x, find the value of a and the value of b. Also, write down the coordinates of the turning point on the graph of y = x^2 - 6x + 1.

Solution

Let's solve the given question step by step.

The equation is:

x26x+1=(xa)2bx^2 - 6x + 1 = (x - a)^2 - b

Part (i) Find the values of aa and bb:

We need to express x26x+1x^2 - 6x + 1 in the form (xa)2b(x - a)^2 - b.

First, expand (xa)2(x - a)^2: (xa)2=x22ax+a2(x - a)^2 = x^2 - 2ax + a^2 So, the equation becomes: x26x+1=x22ax+a2bx^2 - 6x + 1 = x^2 - 2ax + a^2 - b

Now, compare the coefficients of like terms from both sides of the equation.

  • Coefficient of x2x^2 is the same on both sides.

  • For the xx-term: On the left-hand side, the coefficient of xx is 6-6, and on the right-hand side, it is 2a-2a. Therefore: 2a=6a=3-2a = -6 \quad \Rightarrow \quad a = 3

  • For the constant term: On the left-hand side, the constant is 11, and on the right-hand side, it is a2ba^2 - b. Thus: a2b=19b=1b=8a^2 - b = 1 \quad \Rightarrow \quad 9 - b = 1 \quad \Rightarrow \quad b = 8

So, the values are: a=3,b=8a = 3, \quad b = 8

Part (ii) Coordinates of the turning point:

The equation y=x26x+1y = x^2 - 6x + 1 can be rewritten as:

y=(xa)2b=(x3)28y = (x - a)^2 - b = (x - 3)^2 - 8

The turning point (vertex) of a quadratic function y=(xa)2by = (x - a)^2 - b occurs at the point (a,b)(a, -b). Therefore, the coordinates of the turning point are:

(3,8)(3, -8)

Final Answers:

  1. a=3a = 3
  2. b=8b = 8
  3. The coordinates of the turning point are (3,8)(3, -8).

Would you like any further details or explanations? Here are some related questions to explore:

  1. What is the general method to complete the square for a quadratic equation?
  2. How does the form (xa)2b(x - a)^2 - b help in identifying the turning point?
  3. What is the significance of the discriminant in quadratic equations?
  4. How can you find the axis of symmetry for a quadratic function?
  5. How does the graph of y=x26x+1y = x^2 - 6x + 1 compare to the graph of y=x2y = x^2?

Tip: Completing the square is a useful technique for rewriting quadratics to easily identify key features like the vertex (turning point).

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Math Problem Analysis

Mathematical Concepts

Quadratic Equations
Completing the Square
Vertex Form of a Quadratic Equation

Formulas

Standard form of a quadratic: ax^2 + bx + c
Vertex form: (x - a)^2 - b

Theorems

Vertex formula of a quadratic equation
Method of completing the square

Suitable Grade Level

Grades 9-11