Help me solve this maths question please. I want to make sure I am correct :)

Find the equation of the curve: A quadratic curve passes through O(0,0) and its gradient at the point (-2,3) is -1.

Integration

Reply 1

lerjj

13

Original post by CTinTin14

Find the equation of the curve: A quadratic curve passes through O(0,0) and its gradient at the point (-2,3) is -1.

Integration

have you made a start on this? tell us what you've already worked out.

Reply 2

Xin Xang

14

Original post by CTinTin14

Find the equation of the curve: A quadratic curve passes through O(0,0) and its gradient at the point (-2,3) is -1.

Integration

Consider the quadratic:

How can you use this to find an equation for the gradient and also consider what happens when you substitute (0,0) into this equation ?

Reply 3

aoxa

11

I'm not really sure what you're asking? You would integrate if you wanted to find the area under the curve, and the question seems to be asking you to find the equation of the curve.

Reply 4

Mentedya

One of the solutions to y=0 is x=0 so the quadratic would have the form y=a(x^2)+bx which is the same as y=x(ax+b). Next sub in (-2,3) to get 3=4a-2b. Now you need to differentiate y=a(x^2)+bx which gives dy/dx=2ax+b. At x=-2 dy/dx is -1 so we have -4a+b=-1.
Then you have two simultaneous equations that you can solve to get a and b, no integration required.

Reply 5

Xin Xang

14

Original post by Mentedya

One of the solutions to y=0 is x=0 so the quadratic would have the form y=a(x^2)+bx which is the same as y=x(ax+b). Next sub in (-2,3) to get 3=4a-2b. Now you need to differentiate y=a(x^2)+bx which gives dy/dx=2ax+b. At x=-2 dy/dx is -1 so we have -4a+b=-1.
Then you have two simultaneous equations that you can solve to get a and b, no integration required.

You're not supposed to just give the answer. Its a student forum, not an answer forum.

Help me solve this maths question please. I want to make sure I am correct :)

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