Which of the following quadratic functions has a graph that opens downward?

***Choose ALL that apply
please explain!! Thanks :)

(will attach answer choices in a sec!)

Question

Which of the following quadratic functions has a graph that opens downward?

***Choose ALL that apply
please explain!! Thanks :)

(will attach answer choices in a sec!)

anonymous · Answer

answer choices A,B,C,D from top to bottom.
Choose ALL that apply :)

anonymous · Answer

in $$ax^2+bx+c$$
a>0 
|dw:1350133160322:dw|
a<0|dw:1350133187282:dw|

anonymous · Answer

C,D

anonymous · Answer

so when a<0, it is downwards?

anonymous · Answer

and how did u get C,D?? are those the answers??

anonymous · Answer

open equation C 
$$y=-(5+2x^2)=-2x^2-5$$
and re arrange D$$y=60-15x^2=-15x^2+60$$

anonymous · Answer

notice that if the coefficient of $$x^2$$
is negetive then the graph is sad
|dw:1350133494425:dw|

anonymous · Answer

A,B have positive coefficient
C,D have negetive coefficient

anonymous · Answer

okay, so that makes my answers C and D?? because of what u wrote above?? 
so equation C. y=-(5+2x^2)
and D. y=60x-15x^2
are my answers??
C and D?? :D

anonymous · Answer

@wio and @jonask??? are my answers C and D then?? :D

anonymous · Answer

yes do you see why

anonymous · Answer

yes, because the equations are downward since they have negative coefficients.... is that right?? :D

anonymous · Answer

C and D is correct.

anonymous · Answer

If the coefficient before the $x^2$ is negative then it opens downwards as @Jonask said.

anonymous · Answer

okay, awesome!! i see now :) thanks :)

anonymous · Answer

@jonask can u pls give @wio a medal? :) i can only give one :/

anonymous · Answer

thanks for the help!! :D