\[-3^2 =-9\]
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
\[cos^{-1} \: 0.2\]