Помогите номер 3, 4, 5

4. если х=2, то 3х-х²=3*2-2²=6-4=2
5. $\frac{ 3^{15}}{ 3^{9}* 9 ^{2} } = \frac{3^{15}}{3^{9}* (3^{2})^{2} } =$
= $\frac{ 3^{15} }{ 3^{9}* 3^{4} } = \frac{3^{15}}{ 3^{13} } = 3^{15-13} = 3^{2} =9$
б) $\frac{ 8^{5}* 3^{15} }{ 6^{13} } = \frac{ (2^{3})^{5}*3^{15} }{6^{13}} =$
$\frac{ 2^{15}* 3^{15} }{ 6^{13} } = \frac{(2*3)^{15} }{6^{13}} = \frac{6^{15}}{6^{13}} = 6^{15-13} =$
$6^{2} =36$