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C4 double angle proof exam question help!

question being uploaded..

OP

I dont understand the second step written in pencil how in the mark scheme it just multiplies 2sinxcosx by cosx on numerator and denominator. How is it not 2sinxcos^2x - sinx?

Original post by AndyOC

I dont understand the second step written in pencil how in the mark scheme it just multiplies 2sinxcosx by cosx on numerator and denominator. How is it not 2sinxcos^2x - sinx?

Only the first term was multiplied by

cos(x)

\frac{2sin(x)cos(x)}{1}*\frac{cos(x)}{cos(x)}

(edited 8 years ago)

OP

Original post by 123Master321

Only the first fraction was multiplied by

cos(x)

\frac{2sin(x)cos(x)}{1}*\frac{cos(x)}{cos(x)}

I didn't realise you could just do that, is it the same with all trig proof questions then?

Original post by AndyOC

I didn't realise you could just do that, is it the same with all trig proof questions then?

The reason you can do that is because you are effectively only multiplying by 1 as

\frac{cos(x)}{cos(x)}=1

Im not sure what you mean " is it the same with all trig proof questions then"

OP

Original post by 123Master321

The reason you can do that is because you are effectively only multiplying by 1 as

\frac{cos(x)}{cos(x)}=1

Im not sure what you mean " is it the same with all trig proof questions then"

Ah yeah I see now don't worry, I was just a bit confused because i didn't really think about it like that. Thanks for the help!

Original post by AndyOC

Ah yeah I see now don't worry, I was just a bit confused because i didn't really think about it like that. Thanks for the help!

No problem!! Glad I could help

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