Calc AB

[kentw233]

Suppose the point (1,3) is on the graph of f(x)=ax^2+bx. Also suppose that (1,3) is a relative maximum of f(x). Find a and b. show all work for credit.

answers are a=-3
and b=6

i have a test tomorrow and no one has been able to help me. This is the only problem on review I can't get.

 

[mmm4444bot]

Do you know how to determine f'(x) ?

You're given the coordinates at a local maximum on the graph of function f.

Because that point is a maximum, the derivative of function f is zero there.

In other words, f'(1) = 0

Use this equation, substituting x=1 into your derivative expression -- you'll have an equation in a and b.

Substitute the coordinates (1,3) into the given equation defining f(x) -- you'll have a second equation in a and b.

Solve the system of two equations for a and b.

Questions? Work to show? :cool: