Question

Find the linear approximation of the f(x,y)=x+yx​ at the point (1,6)

Answer 1

`L(x,y)=f(a,b)+f_x'(a,b)(x-a)+f_y'(a,b)(y-b)\\\\f(x,y)=x+yx\\(a,b)=(1,6)\\\\f(1,6)=1+6\cdot1=7\\f'_x(x,y)=1+y\\f'_x(1,6)=1+6=7\\f'_y(x,y)=x\\f'_y(1,6)=1\\\\L(1,6)=7+7\cdot(x-1)+1\cdot(y-6)\\L(1,6)=7+7x-7+y-6\\L(1,6)=7x+y-6`