Simplying trig q (1 Viewer)

[=)(=]

For somereason when i use the sum to products i get b

 

[ExtremelyBoredUser]

View attachment 34812
For somereason when i use the sum to products i get b

Are you sure? I'm not getting b. Could you show your working out? I'm getting C

I'm using the formulas (on reference sheet)

cos(A-B) - cos(A+B) = 2sin(A)sin(B)
sin(A+B) + sin(A-B) = 2sin(A)cos(B)

to simplify


Working out for anyone interested'

For numerator; cos3x - cos5x

A - B = 3x
A + B = 5x
-------------
2A = 8x therefore A = 4x, hence B = x

cos3x - cos5x = 2sin(4x)sin(x)

For denominator; sin3x + sin5x

A + B = 3x
A - B = 5x
-------------
2A = 8x therefore A = 4x, hence B = -x

sin3x + sin5x = 2sin(4x)cos(-x) = 2sin(4x)cos(x)

So num/denom:

2sin(4x)sin(x) divided by 2sin(4x)cos(x) = sinx/cosx = tanx

 

[5uckerberg]

This should give you c.

 

[5uckerberg]

Probably @=)(= had some difficulty with the signs.

 

[ExtremelyBoredUser]

Probably accidentally took cos(-x) = -cos(x) if he did that approach

 

[=)(=]

Yeah lol i messed up cause I factored out -1 on the top so it was in the from -2sinasinb=cos(a+b)-cos(a-b)

Thanks for the correction guys

 

[ExtremelyBoredUser]

Yeah lol i messed up cause I factored out -1 on the top so it was in the from -2sinasinb=cos(a+b)-cos(a-b)

Thanks for the correction guys

all goods happens to everyone

 

[=)(=]

those damn sum to products with their hard to memorise signs hhahaahha

 

[yanujw]

those damn sum to products with their hard to memorise signs hhahaahha

Memorise? I'll be honest, I remember basically everything on the formula sheet, but never product-to-sums. Just remember the sheet is always there for your reference

 

[=)(=]

Thanks will keep that in mind

 

[ExtremelyBoredUser]

those damn sum to products with their hard to memorise signs hhahaahha

I can memorise a 1500 word essay for economics, word for word but as soon as it comes to maths I procrastinate memorising sums to products lmao but the best way is probably creating a mnemonic or something that'll make you remember the formulas. Prolly the only thing I'd flip to the formula sheet for haha