mathematics (1 Viewer)

[chels777]

hi guys im not the greatest at mathematics and have kind of let it slide the whole year because i have convinced myself it wont count
im having issues with a question from the 2008 hsc
differentiate In(cosx)
it must be easy because it is a question 3 but i dont think i know the rule im basically stuck on how to approach it can anyone help?

 

[SpiralFlex]

Remember this,



Or in other words, the derivative of the natural logarithmic function is done by putting on top of

Hence in your case,



We know that the derivative of is

Hence,

 

[danjw]

d/dx(lnf(x)) = f'(x)/f(x)

Therefore ln(cosx)= -sinx/cosx

=-tanx

Spi I think you left out a negative sin.

 

[gunat61]

okay d/dx ln(cosx) = 1/sinx multiplied by the differentiation of cosx (which is -sinx). therefore, it's -sinx/cosx = -tanx

 

[SpiralFlex]

d/dx(lnf(x)) = f'(x)/f(x)

Therefore ln(cosx)= -sinx/cosx

=-tanx

Spi I think you left out a negative sin.

I was editing it still...

 

[danjw]

Wasn't aware, sorry about that.

 

[SpiralFlex]

Wasn't aware, sorry about that.

Do not worry human.

 

[xMorrow]

I was just doing this test and wasn't too sure about this question, glad I got it right

 

[chels777]

thanks guys that really helps so many little things i have to remember btw does anyone know the raw marks you would need for a band 5 roughly

 

[xMorrow]

~60%