So yeah, I didn't pay attention in school, and now I'm self teaching. My math book gives me this equation:

(y/2+z/3) * (y/2+z/3)

My logic is as follows:

y/2*y/2=y^2/4

y/2*z/3=yz/6

z/3*z/3= z^2/9

So my mid point is y^2/4 + yz/6 + yz/6 + z^2/9

Which simplifies to y^2/4 + yz/3 + z^2/9

My book OTOH tells me that the equation simplifies to y^2/4 + y^z/3 + z^2/9

Plugging in numbers for the variables leads me to...frustration I just need a brief explanation as to why the problem simplifies as it does.

Danke.