2. (70 points) Are the following statements true or false? If true, prove it and explain which method(s) of proof you have used; if false, disprove it. a. For every positive integer n,(n2+11n+11) is a prime number. b. For any integer x1, if x2+4x3 is odd, then x must be even. c. There are no solutions in positive integers x and y to the equation x4+y4=550