<span>А) х^2+6х-7=x^2+2*3x+9-9-7=(x+3)^2-16
</span><span>Б) х^2-6х=x^2-2*3x+9-9=(x-3)^2-9</span>
2x+x=-20
3x= -20
2
x = - 6 __
3
(b-3)(b-4)-(b+4)²=b²-4b-3b+12-(b²+8b+16)=
=b²-7b+12-b²-8b-16=-15b-4
<span>z=arctg(x^2+y^2)
z`(x)=1*2x/(1+(x^2+y^2)^2)=</span>2x/(1+x^4+y^4+2x^2y^2)<span>
z`(y)=1*2y/</span>(1+(x^2+y^2)^2)=2y/(1+x^4+y^4+2x^2y^2)