Can anyone help me with this Trig Identity double angle question?

Hi guys I am having real difficulty cracking this tri identity.

square root 2 sin (theta- pi/4) = sin theta - cos theta

I have attempted it ever so slightly but am struggling at transposing the LHS to match the RHS

pi/4 I figured was square root 2/2 as a trigonometric value, I thought that this would have some influenece in cancelling out the initial square root of 2.

Another thought was to calculate the pi/4 = 0.785 and also square root of 2 sin = 1.414.

Again I am not entirely sure which path or direction to take with this one, any help would be massively appreciated.

Thanks in advance

(Wink)