I'm not sure if I've understood my textbook correctly. Can you tell me if my current understanding is correct:

- in a single slit diffraction theres a

**wide central fringe** which is twice as wide as all the other outer fringes

- if we had a double slit diffraction instead of a single slit, we would see fringes

**within ** the area that would've been occupied by the

**wide central fringe**
Below is a diagram in my textbook showing intensity distribution of young's fringes, I don't really understand it. Is the blue line supposed to represent the fringes of a single slit diffraction, and the solid red line is representing the fringes of a double slit? I also don't understand at all what the dashed lines in the background are about

(btw this is all high school level physics)