(2) because x+y = 4; So the square of (x+y) = 16, that is, the square of x+the square of y +2xy= 16.

So 2xy= 16- 10=6, so the square of (x-y) = the square of x+y -4xy= 16- 12=4.

(3) The original formula = the square of a+the square of b-2ab+the square of b+the square of c-2bc.

Square of =+square of =(a-b-c)

=0

Therefore, this equation holds only when a-b=0 and b-c=0.

That is, a = b = CB = C.

So the triangle is an equilateral triangle.

(4) that is so-and-so n power, such as 2 3, that is, 2 to the third power (which is much more convenient)

4x^3+4x^2y+xy^2)

=x(4x^2+4xy+y^2)

=x(2x+y)^2

So the algebraic expression (1) 2x+y (2) 2x 2+xy.

(5)a^(mn)=a^(m+n)

That is, Mn = m+n.

Divide both sides by mn at the same time

That is1=1/n+1/m.

Obviously, the above formula holds if and only if n=m=2.

When m=n=0, it is obviously true, but it is not a positive integer.

So when m=n=2, the meaning of the problem is satisfied.

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