(с-3)(с+4)-с²

To simplify the expression \((c - 3)(c + 4) - c^2\), we can first expand the product \((c - 3)(c + 4)\).

Using the distributive property (also known as the FOIL method for binomials):

\[ (c - 3)(c + 4) = c \cdot c + c \cdot 4 - 3 \cdot c - 3 \cdot 4 \]

This simplifies to:

\[ c^2 + 4c - 3c - 12 \]

Combining like terms gives us:

\[ c^2 + (4c - 3c) - 12 = c^2 + c - 12 \]

Now we can substitute this back into the original expression:

\[ (c^2 + c - 12) - c^2 \]

Now, subtract \(c^2\):

\[ c^2 + c - 12 - c^2 = c - 12 \]

So the simplified expression is:

\[ \boxed{c - 12} \]