Maths help: graph equations

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thread starter Jamajax May 13 2009 + PM | QUOTE | PERMALINK | REPORT

I've got this question in an exam paper and I can't figure out this question. Been through my books and everything so I resorted to the interwebs. a>0 b>0 Write down the letter of the sketch which is the graph og y=b-ax^2 I know that because a is positive, its a U shape not an n shape There are 2 graphs that are U shaped, the low point of one is positive and the low point of the other is negative but I don't know which one it is or why Any help is appreciated

FatelessNexus 05/13/09 + PM | QUOTE | PERMALINK | REPORT

Hmm...I'm more used to seeing y=ax^2+bx+c style Let's see: Rearrange equation to y=-ax^2+b a is positive, yet the negative sign in front makes a negative, giving the graph an upside-down U shape. b is positive, and since it's a constant, shift the graph up b units. It seems like you would have a high point at (0,b) not low points o.o unless I read the question wrong somehow

giles200399 May 13 2009 + PM | QUOTE | PERMALINK | REPORT

y = b - ax^2 This means its a "n" curve.... Remember there's a -ve sign in your equation. The curve will cut the x-axis at x = +/- sqrt (b/a) (ie when y = 0). The curve will cut the y-axis at y = b (ie when x = 0). @ DawningRose: Yeah you didn't read the question wrong, he just didn't get the shape of the curve right. ie it is a maximum point, no minimum point.

maxxtro May 13 2009 + PM | QUOTE | PERMALINK | REPORT

EDIT:Read the question wrong,my bad.

Jamajax 05/13/09 + PM | QUOTE | PERMALINK | REPORT

FatelessNexus said: "Hmm...I'm more used to seeing y=ax^2+bx+c style Let's see: Rearrange equation to y=-ax^2+b a is positive, yet the negative sign in front makes a negative, giving the graph an upside-down U shape. b is positive, and since it's a constant, shift the graph up b units. It seems like you would have a high point at (0,b) not low points o.o unless I read the question wrong somehow" No, I thought that because the question said a and b were positive it would have a U shape, not upside down so yeah its the high point. Sooo if b is positive then the high point in the graph is positive... I think w00pz, thanks for the help posters :P :D:D