Hi there,

I'm looking for some help on two questions, I think I have the first one but would like confirmation that I'm correct. The second one I'm getting slightly confused with.

thanks.

Solve the following for 0 <= x <= pi

(i) Sin 5x - sin 2x = 0

(ii) Cos 5x + Sin 5x + Cos 3x + Sin 3x = 0

Okay,

For (i):

I use the sum and difference identities and get:

2cos (7x/2) * sin (3x/2) = 0

Therefore when either of these equal zero the statement is true.

Therefore,

2cos (7x/2) = 0

x = pi/2 as a general solution and calculate the next six.

the divide by 7/2 to give x and select the ones in the correct range which are:

pi/7, 3pi/7, 5pi/7 & pi

Do the same for Sine (3x/2) = 0 and I get 0 & 2pi/3.

These are all the solutions.

Is this correct??

(ii) It looks like this is a case of two sum and difference identities combined but I just get into a mess.

Can anyone help???

many thanks,

D