why is -9^2= -81

Thanks Rosala

In this instance -9 is thought of as -1*9 and so it is reasonable that -1*9^2 = -1*81= -81

This is because you do exponents before you do multiplication with order of operation.  ;)

There are a lot of maths conventions like this.  someone had to say how this wuld be interpreted and this is what was chosen.

This example might make more sense to you,

20-3^2 = 20-9 = 11

see, it is 20-(3^2) =11    not     20+(-3)^2 which would be 29

-9^2 is -81 and not just 81 becoz there is a minus sign in nine which we will also include while we solve the square so thats why just becoz nine has a minus sign , the sign is also included in our answer after we solve the square and if nine didnt have a minus sign so it means there is nothing for us to include in our answer thats why 9^2 is 81 

hope u have understood by now but if not then pls be free to ask!

hope this helps!

yeah but isint -9^2 the same thing as -9 x -9 which equals 81? o.O

woooow nice explanation!! i got it thanks melody

yeah nice explaination melody!

but............i think.......that has to be easy for a teacher isnt it and im a student!

Rosala, you did a good job too.  We all learn of each other.   

yes we both did a good job!i was just joking with you!