## Common Calculator 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.The answer is

\[cos^{-1} \: 0.2\]