I meant to share more on factor Formulae today. However, a few students are not so sure how to get the R-formulae correctly during their preliminary exams recently. So I thought that I’ll share how they can derive the R-Formulae from the MF26.

The following is the R-Formulae which students should have memorised. It is under assumed knowledge, just saying…

where and for and is acute.

So here, I’ll write the addition formulae that’s found in MF26.

I’ll use an example I discussed previously.

Write as a single trigonometric function exactly.

Lets consider the formulae from MF26.

We can let

Putting things together, we have that

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[…] as it is from secondary Add Math. This formulae is not given in MF26, although students can derive it out using existing formulae in […]