Help

[low dock]

So I know the derivative of f(x) is 2ax + b, however I'm unsure how to know what line it is out of the options given, can someone help?

[silver lance]

notice that a<0

[low dock]

how so?

[quiet zenith]

The quadratic is concave down so a is less than 0

[low dock]

I see, I forgot alot about stuff like that with graphs

lol

So if a < 0

y = 2(-1)x + b

or -2x + b

then if x < 0 then y will be higher on the axis?

but how would you know if it's No. 1 or No. 2

[quiet zenith]

In the function,
f(x) = ax^2 + bx + c
f’(x) = 2ax + bx

In the graph we see a is negative

So 2(-a)x

The derivative must have a decreasing slope if thats the case

Which we can eliminate c and d

For a and b, their difference is mainly their y intercepts

[low dock]

so how do we know if its a or b

[quiet zenith]

In b the y intercept is negative, and in a it’s positive

In 2(-a)x + b, the y intercept is positive