is square root of 81?

= √(81)
= 9 or - 9

Answer: 9 or - 9

Proof:
= 9 * 9
= 81

= - 9 * - 9
= 81

Who cares if he doesn't believe? Ask him for an answer with proof and whatever answer he gives you other than ours, don't believe him either. Just brand him an imbecile or a moron.

81 has two square roots, 9 and -9, because you can square each of those numbers with 81 being the result.

9 (as opposed to -9) has become known as the "principal" square root. When you simply see sqrt(81), or the equivalent using a radical symbol, you are to assume it has a value of 9, not -9 or two values of +/- 9.

So, in a sense, you're both right, just with different definitions of the word "right."

9.

yes.

it is +-9

Technically it is ± 9 but often it is assumed that it is only the + ve square root that is required.

±√81
= ±√(9^2)
= ±9 (+9 or -9)

√81 = ± 9

its +/- 9 because -9 * -9 = 81 and so does 9 * 9 = 81

so tell ur bro that he's wrong ;D

The square root of 81 is 9 or -9

The square root of -81 is 9i (imaginary numbers, if you haven't learned that yet)

9 squared is 81

-9 squared is 81

the answer can be either positive 9 or negative 9.