chose the correct quadratic equation using the graph

Question

chose the  correct quadratic equation  using the graph

anonymous · Answer

attachment

anonymous · Answer

I think its either a or b

cwrw238 · Answer

thats correct it opens upwards so the coefficient of x^2 is positive

anonymous · Answer

yes but the bx part of the equation I dont know how to get it

ganeshie8 · Answer

to further nail down, find the x coordinate of vertex from each option : $\frac{-b}{2a}$ and see which one closely matches

anonymous · Answer

ok so its b

ganeshie8 · Answer

yup !

anonymous · Answer

when I used   -b/2a to get the x-coordinate I got -2.5  for  B  which is best on the graph

anonymous · Answer

thanks everyone, really appreciate your help :)

ganeshie8 · Answer

for A, u wud get -15/2 which is -7.5 which is no way near to the vertex in graph...

anonymous · Answer

true :)

ganeshie8 · Answer

good work !

whpalmer4 · Answer

You can also get a clue by looking at easy values like x = 0, x = 1.  x=0 doesn't help in this case because they all have the same value for $c$, but $x=1$ rules out all the wrong answers pretty easily.

anonymous · Answer

I see , this is truly correct when I looked at the graph @whpalmer4

whpalmer4 · Answer

for a vertex on the left side of the y-axis, you need to have the same sign for the x^2 and the x terms.

anonymous · Answer

thank you :)

whpalmer4 · Answer

there are a number of little observations like that which will become second nature if you pay attention, and help you quickly find (or verify) the right answer.