How to get from 64sin^2(t)cos^2(t) to 8-8cos4t ?

Mark scheme goes from 64sin^2(t)cos^2(t) to 8-8cos4 without showing how. Guessing it's got something to do with double angle formulae but can't think how. From Edexcel 2022 paper 1

Thanks!

Reply 1

tonyiptony

Might be easier if you do it the other way round...

or there might be previous parts that help you reach this conclusion.

But moral of the story - solution guides don't help you as much as you think.

Reply 2

davros

Original post by emile_d

Mark scheme goes from 64sin^2(t)cos^2(t) to 8-8cos4 without showing how. Guessing it's got something to do with double angle formulae but can't think how. From Edexcel 2022 paper 1

Thanks!

can you write the LHS as a perfect square? Do you recognize the thing that's squared as a multiple of a standard double angle formula?
You will also need the result that links sin^2A to cos(2A) :smile: