C = 1/a + 1/a² + 1/a³
C = (a²+a)/a³ + 1/a³
C = (a²+a+1)/a³
D = 1/(a²b⁵) + 1/(a³b³)
D = (a²b⁵+a³b³)/(a⁵b⁸)
E = 2a/(b³c²) + 3b/a²c³
E = (2a³c³+3b⁴c²)/(a²b³c⁵)
F = 15a⁵b³c⁵-35a²b⁶c⁴+10a⁵b⁴c²
F = 5a²b³c²×3a³c³-5a²b³c²×7b³c²+5a²b³c²×a³b
F = 5a²b³c²( 3a³c³ - 7b³c² + a³b )