Hard4 marksStructured
AQA GCSE · Question 16 · Algebra
Solve (x + 2)(x - 5) = 6x
Solve (x + 2)(x - 5) = 6x
How to approach this question
1. First, expand the brackets on the left-hand side of the equation.
2. Rearrange the equation so that all terms are on one side, equal to zero. This will give you a standard quadratic equation in the form ax² + bx + c = 0.
3. Solve the resulting quadratic equation. You can do this by either factorising, completing the square, or using the quadratic formula.
4. Remember that a quadratic equation usually has two solutions.
Full Answer
**Step 1: Expand the brackets.**
(x + 2)(x - 5) = x(x - 5) + 2(x - 5)
= x² - 5x + 2x - 10
= x² - 3x - 10
**Step 2: Rearrange the equation into the standard quadratic form ax² + bx + c = 0.**
The equation is now:
x² - 3x - 10 = 6x
Subtract 6x from both sides to make the right side equal to zero:
x² - 3x - 6x - 10 = 0
x² - 9x - 10 = 0
**Step 3: Solve the quadratic equation.**
We can solve this by factorising or using the quadratic formula.
*Method 1: Factorising*
We need two numbers that multiply to make -10 and add to make -9.
The numbers are -10 and +1.
So, we can factorise the equation as:
(x - 10)(x + 1) = 0
For the product to be zero, one of the factors must be zero.
Either x - 10 = 0 => x = 10
Or x + 1 = 0 => x = -1
*Method 2: Quadratic Formula*
For x² - 9x - 10 = 0, we have a=1, b=-9, c=-10.
x = [-b ± √(b² - 4ac)] / 2a
x = [ -(-9) ± √((-9)² - 4(1)(-10)) ] / (2 * 1)
x = [ 9 ± √(81 + 40) ] / 2
x = [ 9 ± √121 ] / 2
x = [ 9 ± 11 ] / 2
So, x = (9 + 11) / 2 = 20 / 2 = 10
Or, x = (9 - 11) / 2 = -2 / 2 = -1
**Answer: x = 10 and x = -1**
The given equation is (x + 2)(x - 5) = 6x.
**1. Expand the brackets:**
We use the FOIL method (First, Outer, Inner, Last):
(x * x) + (x * -5) + (2 * x) + (2 * -5)
= x² - 5x + 2x - 10
Combine the x terms:
= x² - 3x - 10
So the equation is now: x² - 3x - 10 = 6x
**2. Rearrange to standard quadratic form (ax² + bx + c = 0):**
Subtract 6x from both sides:
x² - 3x - 6x - 10 = 0
x² - 9x - 10 = 0
**3. Solve the quadratic equation:**
We can factorise this expression. We are looking for two numbers that multiply to give -10 and add to give -9. These numbers are -10 and +1.
So, the equation becomes:
(x - 10)(x + 1) = 0
This gives two possible solutions:
- If x - 10 = 0, then x = 10.
- If x + 1 = 0, then x = -1.
The solutions are x = 10 and x = -1.
Common mistakes
✗ Errors in expanding the brackets, especially with negative signs.
✗ Incorrectly rearranging the equation (e.g., adding 6x instead of subtracting).
✗ Errors in factorising or in applying the quadratic formula.
✗ Finding only one of the two solutions.
Practice the full AQA GCSE Maths Higher Tier Paper 2 Calculator
33 questions · hints · full answers · grading
More questions from this exam
Q01.1Choose a word from the list below to complete the sentence.
<br>
<br>
arc, centre, ci...EasyQ01.2Choose a word from the list below to complete the sentence.
<br>
<br>
arc, centre, ci...EasyQ01.3Choose a word from the list below to complete the sentence.
<br>
<br>
arc, centre, ci...EasyQ02Here is a grouped frequency table.
<br>
<br>
Work out an estimate of the mean value.MediumQ03In the grid below, shade one quarter of the squares so that the grid has exactly two lines of sym...Easy
Expert