Question 164619
1) (7a^4+8ab+b^2)+(-5a^4-8ab-4b^2)

=7a^4+8ab+b^2-5a^4-8ab-4b^2
=(7a^4-5a^4)+(8ab-8ab)+(b^2-4b^2)
=2a^4+0-3b^2
=2a^4-3b^2 Ans

2) (6r+2s-1)-(4r-7s+1)
=(6r-4r)+(2s+7s)-(1+1)
=2r+9s-2 Ans

3) (7a^2b+4ab)+(9a^2b-8ab)-(11a^2b+14ab)
=(7a^2b+9a^2b-11a^2b)+(4ab-8ab-14ab)
=5a^2b-18ab

4) (-5x^3+2y^3)-(15x^3-7x^2y+8xy^2-4y^3)
=(-5x^3-15x^3)+(2y^3-4y^3)-7x^2y+8xy^2
=-20x^3-2y^3-7x^2y+8xy^2 Ans