18) [tex]19m^8n^8-\left(4m^5n\right)\left(3m^3n^7\right)[/tex]
[tex]=19m^8n^8-4m^5n\cdot \:3m^3n^7[/tex]
[tex]=19m^8n^8-12m^8n^8[/tex]
[tex]=7m^8n^8[/tex]
19) [tex]\left(-5cd\right)\left(-3c^4d\right)-\left(7c^2d^2\right)\left(2c^3\right)[/tex]
[tex]=5cd\cdot \:3c^4d-7c^2d^2\cdot \:2c^3[/tex]
[tex]=15c^5d^2-14c^5d^2[/tex]
[tex]=c^5d^2[/tex]
