Answer
$-0.98x^2+2.8x+1.86
$
Work Step by Step
Removing the parenthesis and then combining like terms, the given expression, $
(-0.98x^2-1.56x+5.57)+(4.36x-3.71)
,$ is equivalent to
\begin{array}{l}\require{cancel}
-0.98x^2-1.56x+5.57+4.36x-3.71
\\=
-0.98x^2+(-1.56x+4.36x)+(5.57-3.71)
\\=
-0.98x^2+2.8x+1.86
.\end{array}
Let
\begin{array}{l}\require{cancel}Y_1=
(-0.98x^2-1.56x+5.57)+(4.36x-3.71)
,\\Y_2=
-0.98x^2+2.8x+1.86
.\end{array}
Using a graphing calculator, the graphs of $Y_1$ (dotted graph) and $Y_2$ (solid graph) are shown below. Since the graphs overlap, then $Y_2$ is the correct simplification of $Y_1.$
