answer:The original expression can be rewritten as 2(m^2-2mn+n^2)-1, which simplifies to 2(m-n)^2-1. Since m-n=2, the expression becomes 2 times 4 - 1 which equals 7. Therefore, the answer is boxed{7}.

answer:Since circle C_1: (x-a)^2+y^2=4 (a > 0) and circle C_2: x^2+(y- sqrt {5})^2=9 are externally tangent, the distance between the centers of the two circles equals the sum of their radii. Therefore, we can establish the following equation: (0+a)^2+(-sqrt{5}-0)^2=(2+3)^2 Simplifying the equation, we obtain: a^2+5=(5)^2 a^2=25-5 a^2=20 a=sqrt{20}=2sqrt{5} Thus, the value of a is boxed{2sqrt{5}}.

answer:If there were 95 seats in the stadium and 14 were empty, then the number of seats that were occupied is: 95 seats - 14 empty seats = 81 occupied seats Since we know that 52 children went to the track meet, we can subtract that number from the total number of occupied seats to find out how many adults were there: 81 occupied seats - 52 children = 29 adults So, boxed{29} adults went to the track meet.

answer:From the given problem, we have: y'=3x^{2}-3. Let y'=3x^{2}-3 > 0, then x > 1 or x < -1. Therefore, the function y=x^{3}-3x is increasing on (-infty,-1), decreasing on (-1,1), and increasing on (1,+infty). Thus, when x=-1, the function has a maximum value of m=2, and when x=1, the function has a minimum value of n=-2. Therefore, m+n=0. Hence, the correct choice is boxed{A}. Using the derivative tool to solve the problem of finding the extreme values of the function, the key is to use the derivative to find the intervals of monotonicity of the original function, which allows us to determine where the function attains its extreme values, thereby obtaining the answer. The key to solving this problem is to use the derivative tool to find the extreme values of the function. First, determine the range of real numbers x for which the derivative function is greater than 0, then discuss the intervals of monotonicity of the function, and use the method of determining extreme values to find the extreme values of the function, demonstrating the utility of the derivative.