Algebra
⏱ ~3-min readAceMark GuideWhat this topic is really about
First, factorise out the common factor of 2 to get 2 times the quantity x squared minus 4, then apply the difference of two squares to get 2 times x minus 2 times x plus 2. Option B is incorrect because it is not fully factorised, as the first bracket still contains a common factor of 2. Option D is incorrect because expanding it does not yield the original expression.
The quadratic factorises to the product of x minus 2 and x minus 3 equals 0, which yields the solutions x equals 2 or 3. Option C is a common mistake where the signs from the factorised brackets are not reversed to solve for x. Option A is incorrect because those values would satisfy a quadratic that multiplies to negative 6 instead of positive 6.
See the mechanism
Expanding the bracket gives 3x minus 6 equals 5x plus 4, which rearranges to 2x equals negative 10, solving to x equals negative 5. A diagram for this topic isn't available yet — the worked example below walks the same reasoning step by step.
An exam-style question, fully explained
Solve for x: 3(x − 2) = 5x + 4
- Identify what the question tests: Solve for x: 3(x − 2) = 5x + 4.
- Expanding the bracket gives 3x minus 6 equals 5x plus 4, which rearranges to 2x equals negative 10, solving to x equals negative 5.
- Option B is incorrect because it fails to track the negative sign when dividing.
- Option C is wrong because it often arises from a common mistake of failing to multiply the entire bracket by 3.
Traps the examiner sets
- Option B is incorrect because it fails to track the negative sign when dividing.
- First, factorise out the common factor of 2 to get 2 times the quantity x squared minus 4, then apply the difference of two squares to get 2 times x minus 2 times x plus 2.
- Option C is a common mistake where the signs from the factorised brackets are not reversed to solve for x.
- Option D is incorrect because 6 is only the change in the y-coordinates, forgetting to divide by the change in x.
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