a = 3^53 + 3^52 + 3^51
a = 3^51 × (3^2 + 3^1 + 1)
a = 3^51 × ( 9 + 4)
a = 3^51 × 13
__________
b = 2^87 + 2^86 + 7 × 2^85
b = 2^85 × ( 2^2 + 2^1 + 7 × 1)
b = 2^85 × ( 4 + 2 + 7)
b = 2^85 × 13
__________
a = 3^51 × 13 = (3^3)^17 × 13 = 27^17 × 13
b = 2^85 × 13 = (2^5)^17 × 13 = 32^17 × 13
27 < 32 => 27^17 < 32^17 =>
=> 27^17 × 13 < 32^17 × 13 =>
=> a < b
______