Now that’s a CAPTCHA! by ceejayoz on Flickr.
For more details and additional examples of these equation style CAPTCHAs, see random.irb.hr. None are as spectacular as this.
What’s the answer?
This is what ndej77 (also of Flickr) has to say, as a comment:
Haha, wasn’t designed by a mathematician, probably! There is no need for the partial derivative notation because the expression is not multivariate.
35* cos (5x - [pi /2] ) - 3* sin (3x + [pi/2] ) @ x = 2*pi
= 35*(0) - 3*(1)
So -3 is the answer?
I’m not convinced that is correct, not if the derivative stays in the picture.