3. Let points $A(-0.8,4.132), B(1.2,-1.948)$, $C(2.8,-3.932)$ be on the graph of the quadratic function
$$
y=a x^{2}+b x+c
$$

When the point $D$ on the graph has the x-coordinate $x=1.8$, its y-coordinate $y$ is $\qquad$ .
3. -2.992 .

From the given, we have
$$
\left\{\begin{array}{l}
0.64 a-0.8 b+c=4.132, \\
1.44 a+1.2 b+c=-1.948, \\
7.84 a+2.8 b+c=-3.992 .
\end{array}\right.
$$

Solving, we get $a=0.5, b=-3.24, c=1.22$.
Thus, $y=0.5 \times 3.24-3.24 \times 1.8+1.22$ $=-2.992$.