Question

what is the sound of school bell​

Answer 1

Answer:

tan tan tan tan tan tan tan

Answer 2

Answer:

{\sqrt {\frac {1-x^{2}}{1+x^{2}}}}

Explanation:

(a+b)2=a2+2ab+b2 , in the form of square of sum of two variables.

(a−b)2=a2−2ab+b2, negative counterpart of square of sum of two variables.

a2−b2=(a+b)(a−b), this is one of the most useful algebraic relationships.

(a+b)3=a3+3a2b+3ab2+b3, in the form of cube of sum of two variables.

(a+b)3=a3+b3+3ab(a+b), this cube form is used frequently and it is better to remember it as a basic concept.

(a−b)3=a3−3a2b+3ab2−b3, negative counterpart of cube of sum of two variables.

(a−b)3=a3−b3−3ab(a−b), which again is useful.