[tex]e) \ 2k^{2}-(k+3)(2k+4) = 2k^{2}-(2k^{2}+4k+6k+12) =2k^{2}-(2k^{2}+10k+12) =\\\\=2k^{2}-2k^{2}-10k-12 = -10k-12[/tex]
[tex]f) \ -3(a+2b)(a-b)+3a^{2} = -3(a^{2}-ab+2ab-2b^{2})+3a^{2} =\\\\=-3(a^{2}+ab-2b^{2})+3a^{2} = -3a^{2}-3ab+6b^{2}+3a^{2} = 6b^{2}-3ab[/tex]
