Question

Find the differential of
f
(
x
,
y
)
=
x
2
+
y
3
at the point
(
2
,
1
)
.

Answer 1

$f(x,y)=x^2+y^3\implies \left.\cfrac{}{} 2x+3y^2 \right]_{\stackrel{\textit{\small x=2}}{\textit{\small y=1}}}\implies 2(2)+3(1)^2\implies 7$