## Common Calculator Mistakes

Many students make the same calculator mistakes again and again. Here are some of the most common mistakes.

$-3^2 =-9$

In fact
$-3^2 = - 3 \times -3=9$
.
People make this mistake because of the way the calculator is programmed. The simple four function calculator on or most calculators on your phone tell you
$-3^2 =9$
.
This is correct.

Most calculators tell you
$20+10 \% =20.2$
.
This is wrong. In fact
$20+10 \% =22$
.
Again the simple calculator or the calculator on you pnone will give you the correct answer.

A calculator will tell you
$\sqrt{9}=3$
.
This is only partially correct. Every square root has two answers. In fact
$\sqrt{9}=3, -3$
.
Many students think the solutions to
$cos x =0.2$
is
$cos \: 0.2$

It is nut. Look above the cos button on youur calculator, and just above is
$cos^{-1} {}$
which is accessed using the sjift button.
$cos^{-1} \: 0.2$