15. 4ab +2 (a-b)^2= 4ab + 2 (a^2-2ab+b^2)=4ab + 2a^2-4ab+2b^2= 2a^2+2b^2.
16. 3 (x+y)^2 - 6xy= 3 (x^2+2xy+y^2) - 6xy=3x^2+6xy+3y^2-6xy= 3x^2+3y^2.
17. (b+c)(b-c) - b(b-2c)= b^2 - c^2 -b^2+2bc=2bc-c^2.
18. (a-c)(a+c) - c (3a-c)= a^2-c^a - 3ac + c^2= a^2-3ac.
19. a(a+5b) - (a+b)(a-b)= a^2 + 5ab - a^2 +b^2= 5ab+b^2.
20. b(3a-b) - (a-b)(a+b)= 3ab - b^2 -a^2 + b^2= 3ab-a^2.
21. (y+10)(y-2) - 4y(2-3y)= y^2 +8y-20 - 8y+12y^2= 13 y^2-20.
22. (x-1)(x+3) - 2x(1-3x)= x^2 +2x-3 - 2x +6x^2= 7x^2-3.
23. (m+3)^2 - (m-2)(m+2)= m^2+6m+9 - m^2 +4= 6m+13.
24. (y-4)(y+4)- (y-3)^2= y^2-16 - y^2+6y-9= 6y-25.
Удачии!!)))