a) 8t¹² z⁻⁶ - t³z⁻⁹=t³ z⁻⁶(8t⁹ -z⁻³)=t³× 1/z⁶ ×[(2t)³ - 1/z³]=
=t³× 1/z⁶× (2t - 1/z)(4t²+2t/z+1/z²)
b)729a²¹ b⁹ -0,008a¹⁵=a¹⁵×(729a⁶ b⁹ -8/1000)=a¹⁵×[(9a² b³)³ -1/5³]=
=a¹⁵×(9a² b³ -1/5³)(81a⁴b⁶+9a²b³/5+1/25)
am scos factor comun
am folosit formula (a³-b³)=(a-b)(a²+ab+b²)