# O level A-Math: Fatal Mistake In Logarithm Equation You Must Aviod

This is a common mistake I notice in my O level A-Math essential concepts revision workshop.

Solve the following equation:

First, you must identify the type of question since different types of question require different strategies.
It's a different log-log question.
Strategy required: Change base.

Change base formula used.
Reason for changing to base 2: Between changing to base 2 or x, we choose base 2 as x is an unknown, we choose not to work with THE unknown most of the time, don't we?

Since we observe that there is a common term (log2 x),

Did you observe the fatal mistake (It's #7 Common mistake in Logarithm?

The correct way to do the substitution would be:

Solve the quadratic equation for y. Substitute the value back to find x.

Remember to check for validity of answers.

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