How can I get the answer? Thanks!!
更新1:
2. Let t>1 a) Show that t^2 /t-1 ≧ 4 x,y,z ≧ 1 b) x^2 / y-1 + y^2 /z-1 + 2^2 / x-1 ≧ 12 c) x^4 / (y-1)^2 + y^4 / (z-1)^2 + z^2 / (x-1)^2 ≧ 48 3. Prove that 5^n - 25 is divisible by 100 for n ≧ 2. How can I get the answer? Thank a lot!
