(2¹¹-2⁹)/2¹²+(5⁵⁰-5³⁸)/5³⁹=
2⁹(4-1)/2¹²+5³⁸(5¹²-1)/5³⁹=
3/2³+(5¹²-1)/5=3/8+(5¹²-1)/5=
[15+8(5¹²-1)]/40=
(15+8×5¹²-8)/40=
(7+8×5¹²)/40
