Question: I'm worried that this will be a spanner in the works when I'm using a calculator in an exam , I know that $-2^2= 4$ since $(-2) \cdot (-2) = 4 $. So why does my calculator show it as negative 4 ? Does anyone know if there is a way to reset my calculator so it doesn't do this? The make and model is Casio fx-83ES.

Answer: 
$ax +be^x +c\sin(x) =0$, $x=0$ implies $b=0$, $ax+c\sin(x) = 0$, $x=\pi$, $a=0$ thus $c=0$
Suppose
$ax +be^x +c\sin(x) =0
$.

If
$b \ne 0$,
then,
for large enough $x$,
$b e^x$
is much larger than
the other two terms,
which is a contradiction.

Therefore
$b = 0$,
so we have
$ax+c\sin(x)
= 0
$.

Again,
if $a \ne 0$,
we can choose $x$
large enough so that
$|ax| > |c|$.
Since
$|\sin(x)| \le 1$,
this can not hold.

Therefore
$a = 0$,
so that
$c \sin(x) = 0$.

This obviously implies that
$c=0$.

And we are done.