We know how A’levels like to combine a few topics across. We also know how bad trigonometry can be. I was coaching my International Bachelorette (IB) class last week and came across a fairly interesting question. It tests students on their abilities to manage double angle identities. Not a tough question, but definitely good practice 🙂

FYI: All double angle identities are found in MF26.

Here it is…

(a) Show that , .

(b)

(i) Use the double angle identity to show that .

(ii) Show that .

(iii) Hence find the value of exactly.

LHS

(b)

(i)

Let

Let

Since , ,

(ii)

LHS

(iii)

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