Given the function f(x) = x^2 and k = –1, which of the following represents a function opening downward?
f(x) + k
kf(x)
f(x + k)
f(kx)

Question

Given the function f(x) = x^2 and k = –1, which of the following represents a function opening downward?
 f(x) + k
 kf(x)
 f(x + k)
 f(kx)

iwanttogotostanford · Answer

@sleepyhead314 @wolf1728

sleepyhead314 · Answer

the coefficient of x would have to be negative in order for the function to open downward

wolf1728 · Answer

Figured I'd come here but sleepyhead seems to be ding quite well

sleepyhead314 · Answer

since "k" is a negative number

I would assume that they would like for us to multiply "x" with "k" somehow

iwanttogotostanford · Answer

i was thinking it'd be B or D?

sleepyhead314 · Answer

D means that you would replace "kx" into the equation for "x"
that would get you  f(kx) = (-1x)^2
                                            ^^ since this is squared, it would come out as a Positive
so that cannot be right

iwanttogotostanford · Answer

i don't know what it would be...

iwanttogotostanford · Answer

@sleepyhead314

sleepyhead314 · Answer

since it cannot be D

then your other guess may be correct ;)

wolf1728 · Answer

would it be k(fx)

sleepyhead314 · Answer

yes ^

sleepyhead314 · Answer

although the formatting is a bit confusing .-.

wolf1728 · Answer

k = -1 f(x) = x^2 then
k(fx) = -x^2

iwanttogotostanford · Answer

so it would be B??:-)

wolf1728 · Answer

I think it is B

sleepyhead314 · Answer

mhmmm

wolf1728 · Answer

yes as sleepyhead said the formatting is weird

iwanttogotostanford · Answer

thank you both! I will have one more question up and then done!

wolf1728 · Answer

Okay, I'll stay here