$$1.) 2ab+3ac+6abc;-5ab+2bc-5abc;\,3ab-2bc-3ac$$
$$2.) 2x^{2}-2xy+3y^{2};\,4y^{2}+5xy-2x^{2};\,-x^{2}+2xy-6y^{2}$$
$$3.) 3a^{2}-7ab-4b^{2}, -6a^{2}+9ab-3b^{2},4a^{2}+ab+5b^{2}$$
$$4.) x^{2}+xy-y^{2};-z^{2}+yz+y^{2};-x^{2}+xz+z^{2}$$
$$5.) -x^{2}-3xy+3y^{2};3x^{2}+4xy-5y^{2};x^{2}+xy+y^{2}$$
$$6.) x^{3}-x^{2}+x-1;\,2x^{2}-2x+2;-3x^{3}+5x+1$$
$$7.) 2x^{3}-x^{2}-x;\,4x^{3}+8x^{2}+7x;-6x^{3}-6x^{2}+x$$
$$8.) 9x^{2}-7x+5;\,-14x^{2}+15x-6;\,20x^{2}-40x-17$$
$$9.) 10x^{3}+5x+8;\,3x^{3}-4x^{2}-6;\,2x^{3}-2x-3$$
$$10.) a^{3}-ab+bc;\, ab+b^{3}-ac;\, ac-bc+b^{3}$$
$$11.) 5a^{3}-3c^{3}+d^{3};\, b^{3}-2a^{3}+3d^{3};\,4c^{3}-2a^{3}+-3d^{3}$$
$$12.) 6x^{3}-2x+1;\,2x^{3}+x+6;\, x^{2}-7x^{3}+2x-4$$
$$13.) a^{3}-a^{2}+3a;\,3a^{3}-4a^{2}+8a;\,5a^{3}-6a^{2}-11a$$
$$14.) x^{2}+y^{2}-2xy;\,2z^{2}-3y^{2}-4yz;2x^{2}-2z^{2}-3xz$$
$$15.) x^{3}-2y^{3}+x;\, y^{3}-2x^{3}+y;\, x^{2}+2y^{2}-x+y^{3}$$
$$16.) x^{3}+3xy^{2}+3y^{2}x,-3x^{2}y-6xy^{2}-x^{3};\,3x^{2}y+4xy^{2}$$
$$17.) a^{3}+5ab^{2}+b^{3};\, b^{3}-10ab^{2}-a^{3};\,5ab^{2}-2b^{3}+2a^{2}b$$
$$18.) x^{5}-4x^{4}y-5x^{3}y^{3};\,3x^{4}y+2x^{3}y^{3}-6xy^{4};\,3x^{3}y^{3}+6xy^{4}-y^{5}$$
$$19.) a^{3}-4a^{2}b+abc;\, a^{2}b-10abc+c^{3};\, b^{3}+a^{2}b+abc$$