#Help solving using algbera please
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radiant shore
Try writing the parabola in the vertex form. That will allow you to express b and c in terms of a.
After that recall when a quadratic equation has two roots.
distant isle
Try writing the parabola in the vertex form. That will allow you to express b an...
you mean like this:
y = a(x-9)^2-14 ??
radiant shore
you mean like this:
y = a(x-9)^2-14 ??
Yeah.
distant isle
thats what I did and I then solved using the discriminant formula
but idk it doesnt work
radiant shore
Well, first of all, what expressions for b and c did you get?
distant isle
Well, first of all, what expressions for b and c did you get?
b = -18a and c = 81a-14
radiant shore
yea i got 324a^2 +56a -324a^2 > 0
Well, you can simplify that a bit, right?
distant isle
yea but 56a>0 isnt helpful no?
radiant shore
Oh, it is.
You can simplify the inequality a bit more, too.
Well, you get a > 0, right?
radiant shore
Well, we want a + b + c, right?
radiant shore
b = -18a and c = 81a-14
So, knowing this, what is a + b + c?
distant isle
yea i know so based upon that those are the only conclusions which can be made no?
because a is a constance not an integer
radiant shore
Well, a can change, of course.
a + b + c won't have an exact value, but we can put a condition on it.
After all, you're asked what its value could be, not what it is.
So, what is a + b + c in terms of just a?
distant isle
how do you put conditions on c , thats what I dont get
radiant shore
b = -18a and c = 81a-14
We've already expressed b and c in terms of a.
distant isle
yea but we have it as a condition not as a variable were we can just plug them in
the only condition i know of is that b<0
radiant shore
We have a condition a > 0 and b and c expressed in terms of a.
That already puts a condition on a + b + c.
What is a + b + c?
Recall that b = -18a, c = 81a - 14.
distant isle
That already puts a condition on a + b + c.
how does it put a condition
thats were I have been stuck on
radiant shore
Substitute b = -18a and c = 81a - 14 into a + b + c. What do you get?
radiant shore
64a-14 = a + b + c
Yeah, nice!
This implies that a + b + c > -14, and only option D works.
You're welcome!
distant isle
.close
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