## Question

secondary 4 | A Maths

Anyone can contribute an answer, even non-tutors.

##### Kathy

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Thank you

Date Posted: 4 months ago
Views: 19

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1st
Part a, part b
Date Posted: 4 months ago
Kathy
4 months ago
When can I use the U formula for logarithm?
Eric Nicholas K
4 months ago
You will notice that two terms are exactly the same. I let u = log 5 x, for example, to simplify matters because it is easier to see the expressions in that way. It’s not a must to let u be something though.
Kathy
4 months ago
I send u a qns, can you use U formula for Me. Thanks
Eric Nicholas K
4 months ago
For example, if (5^x)^2 - 2 (5^x) + 1 = 0, letting u = 5^x (you can use other letters also) transforms the equation into u^2 - 2u + 1 = 0 which you immediately recognise to be a quadratic equation.

We then solve the quadratic equation followed by solving for x.
Eric Nicholas K
4 months ago
Done up - in that expression we only have x and y after conversion so there is no need to replace x or y by u.