What is the difference if the negative is in parenthesis or if it is not in parenthesis

For number 19, when you see the parenthesis, you must look at everything that’s inside and then square it, as you have done correctly. Without the parenthesis like in number 18, you are only looking at squaring the number 3 as it is the only number directly attached to the square. 3 squared is 9 and then take into account the negative. It would be like multiplying by a negative 1. The final answer would be -9 in this case. Hope this helps! :)

Hey!
For number 18, it is actually -9 because the negative is not included in the parenthesis. 
That means that the - and 3 are not connected. So the square is only for the 3 in this case.
FOr 19, it is 9 because there are parenthesis.
In this case the - and 3 are connected and the square is for the -3. If it is in parenthesis then the number is contained and the square sign will Make is -3 * -3 instead of 3*3

Area of circle = pi * radius^2radius is given to be 1/2 inchespi * (1/2)^2 = pi/4 inches^2 = 0.785 inches^2