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# Another Tangents Question watch

1. The parabola passes through point (1,3) and has the tangent at point (2,1). Find the values of a, b and c.

So far:

f(1) = a + b + c = 3

I'm not sure about this, but if I substitute x = 2 into y = -4x + 9, I can work out what 'y' is. Does that help me find the answer in any way?

Where do I go from here?

Thanks
2. (Original post by gottastudy)
The parabola passes through point (1,3) and has the tangent at point (2,1). Find the values of a, b and c.

So far:

f(1) = a + b + c = 3

I'm not sure about this, but if I substitute x = 2 into y = -4x + 9, I can work out what 'y' is. Does that help me find the answer in any way?

Where do I go from here?

Thanks
3. f'(x) = -4x + 9

To find c, sub a and b into f(x) and input the x and y values.
4. as you know f'(x) it would be really handy if you knew the value of the gradient of the curve at one point.....
5. (Original post by gottastudy)
tangent at point (2,1)

[...]

if I substitute x = 2 into y = -4x + 9, I can work out what 'y' is
You know what y is. It's 1. You're given that information in the question.

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Updated: February 3, 2010
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