Question

17-20. Заранее спасибо

Answer 1

17. 3(x-y)^2=3*(x^2-2xy=y^2)=3x^2-6xy+y^2
18. a^2+(9a^2-6ab+b^2)=a^2+9a^2-6ab+b^2=10a^2-6ab+b^2
19. (a-4)^2+a(a+8)=(a^2-8a+16)+(a^2+8a)=a^2-8a+16+a^2+8a=2a^2+16
20. (a-c)*(a+c)-(a-2c)^2=(a^2-ac+ac-c^2)-(a^2-4ac=4c^2)=a^2-ac+ac-c^2-a^2+4ac-4c^2=-5c^2+4ac