In 2004200520062007, the number that cannot be expressed as the square difference of two integers is?

In 2004200520062007, the number that cannot be expressed as the square difference of two integers is?

two thousand and six
x²-y²=2006
(x+y)(x-y)=1003×2
x+y=1003
X-Y = 2, the equations have no integer solution
x+y=2
X-Y = 1003, the equations have no integer solution

It is known that the three sides of a triangle are three continuous non-zero natural numbers, and the triangle is an obtuse angle triangle

Let these three sides be n, N + 1, N + 2. Let a be the angle that the obtuse angle is n + 2
From cosine theorem
n^2+(n+1)^-2n(n+1)cosA=(n+2)^
2n(n+1)cosA=n^2-2n-3
Because a is an obtuse angle, so cosa

In a right triangle, if the hypotenuse is four times the height of the hypotenuse, the degrees of the two acute angles are ()
A.30°,60° B.15°,75° C.20°,70° D.25°,65°

Let the hypotenuse be 4, the height be 1, and the adjacent edge be √ 15
Then sine theorem: 1 / SiNx = 4 / sin90, find X
x=14.xxx
B is the closest. Choose B