1) x^2-25=x^2-5^2=(х-5)(х+5)
2)16-c^2=4^2-с^2=(4-c)(4+c)
3)a^2-6a+9=(a-3)^2
(у-4)(у+4)-(у-3)^2 = y^2-16-(y^2-6y+9) = y^2-16-y^2+6y-9 = 6y-25
A)y'=(9x²+6x-4)'=18x+6
y'(-1)=-18+6=-12
b)y'=((7x+1)/(4x-3))'=
7(4x-3)-4(7x+1)/(4x-3)²=
(-21-4)/(4x-3)²=-25/(4x-3)²
y(-1)=-25/(-4-3)²=-25/49