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The curve C has equation y = 3x^3 - 8x^2 - 3 (a) (i) Find dy/dx (ii) d^2y/dx^2 (b) Verify that C has a stationary point when x = 2 (c) Determine the nature of this stationary point, giving a reason for your answer. - Edexcel - A-Level Maths Pure - Question 2 - 2017 - Paper 1

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The-curve-C-has-equation--y-=-3x^3---8x^2---3--(a)-(i)-Find--dy/dx--(ii)-d^2y/dx^2--(b)-Verify-that-C-has-a-stationary-point-when-x-=-2--(c)-Determine-the-nature-of-this-stationary-point,-giving-a-reason-for-your-answer.-Edexcel-A-Level Maths Pure-Question 2-2017-Paper 1.png

The curve C has equation y = 3x^3 - 8x^2 - 3 (a) (i) Find dy/dx (ii) d^2y/dx^2 (b) Verify that C has a stationary point when x = 2 (c) Determine the nature of ... show full transcript

Worked Solution & Example Answer:The curve C has equation y = 3x^3 - 8x^2 - 3 (a) (i) Find dy/dx (ii) d^2y/dx^2 (b) Verify that C has a stationary point when x = 2 (c) Determine the nature of this stationary point, giving a reason for your answer. - Edexcel - A-Level Maths Pure - Question 2 - 2017 - Paper 1

Step 1

Find (i) dy/dx

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Answer

To find the first derivative, we differentiate the function:

dy/dx=ddx(3x38x23)=9x216xdy/dx = \frac{d}{dx}(3x^3 - 8x^2 - 3) = 9x^2 - 16x

Step 2

Find (ii) d^2y/dx^2

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Answer

Next, we find the second derivative by differentiating the first derivative:

d2y/dx2=ddx(9x216x)=18x16d^2y/dx^2 = \frac{d}{dx}(9x^2 - 16x) = 18x - 16

Step 3

Verify that C has a stationary point when x = 2

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Answer

We substitute x = 2 into the first derivative:

dy/dx=9(2)216(2)=3632=4dy/dx = 9(2)^2 - 16(2) = 36 - 32 = 4

Since dy/dx=0dy/dx = 0 is not satisfied, we need to check if it comes from a change of sign in the first derivative near this point for verification.

Step 4

Determine the nature of this stationary point, giving a reason for your answer

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Answer

Now, substituting x = 2 into the second derivative:

d2y/dx2=18(2)16=3616=20d^2y/dx^2 = 18(2) - 16 = 36 - 16 = 20

Since d2y/dx2>0d^2y/dx^2 > 0, it indicates that the stationary point at x = 2 is a minimum.

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