The parabola y=-2x^2 + 8x - c has its vertex at (2,5). What is the value of c
select one:
A.0
B.3
C.6
D.9

If y varies directly as x2 and y=6 when x=6, find the constant of variation.

I’m really confused and need your assist me with this question i’ve never been taught

Find the directions in which the function increases and decreases most rapidly at upper p 0p0. then find the derivatives of the function in these directions. f(x,y)equals=x squared plus xy plus y squaredx2+xy+y2, upper p 0p0left parenthesis 1 comma negative 4 right parenthesis