f=7x+8y-xy-z=0
f1`(x-x0)+f2`(y-y0)+f3`(z-z0)=0
f1`=df/dx=7-y; f2`=df/dy=8-x; f3`=df/dz=-1
(7-y)(x-1)+(8-x)(y-1)+(-1)(z-14)=0-уравнение касательной пл-ти
7x-7-xy+y+8y-8+xy+x-z+14=0
8x+9y-z-1=0
4*(31c-17+54d)=124c- 34 + 216 d
1)(620-129*3)-128:4-2=199 2)620-(129*3-128:4)2=263 3)620-129*3-128:(4-2)=297