Positive because a function is beetween and past
The distance between a point

on the given plane and the point (0, 2, 4) is

but since

and

share critical points, we can instead consider the problem of optimizing

subject to

.
The Lagrangian is

with partial derivatives (set equal to 0)




Solve for

:


which gives the critical point

We can confirm that this is a minimum by checking the Hessian matrix of

:


is positive definite (we see its determinant and the determinants of its leading principal minors are positive), which indicates that there is a minimum at this critical point.
At this point, we get a distance from (0, 2, 4) of
4 + 3 * (7 - 2)
4 + 3 * 5
4 + 15
19 <==
Answer :
a. p²+q²=r²
According to the Pythagorean theorem :
p²+q²=r² ,because this is a right triangle and r is the length of the hypotenuse.