My Math Forum (http://mymathforum.com/math-forums.php)
-   Calculus (http://mymathforum.com/calculus/)

 ashleybouchakian October 31st, 2017 06:57 PM

f(x)=ax^2+c
dy/dx=2ax

Point A (-2,5) lies on the graph of y=f(x). the gradient of the tangent to this graph at A is -6. Find the value of a and c.

 greg1313 October 31st, 2017 07:09 PM

Where are you having difficulty? The problem can be solved by straightforward substitution.

\$\$f'(-2)=2a(-2) = -6\$\$

Can you continue?

 ashleybouchakian October 31st, 2017 07:11 PM

can you please finish it? I am not sure why, but I am so confused on finding both a and c. I have been doing math all day

 Country Boy November 2nd, 2017 03:41 AM

Quote:
 Originally Posted by ashleybouchakian (Post 583346) f(x)=ax^2+c dy/dx=2ax Point A (-2,5) lies on the graph of y=f(x). the gradient of the tangent to this graph at A is -6. Find the value of a and c.
Since "(-2, 5) lies on the graph", f(-2)= a(4)+ c= 5. The "gradient of the tangent" is 2a= -6. Find a then put that value into the first equation and find c.

 All times are GMT -8. The time now is 12:11 AM.