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# Math Edexcel C2 Differentiation watch

1. Hi.

pg 152 of c2 Edexcel book,
the diagram shows the part of the curve with equation y=5-0.5x^2 for which y is greather than or equal to 0.
O is (0,0)
a. show that OP^2 = 1/4x^4 - 4x^2 +25

Didn't get this one right... i got x^2 + 25 -1/4x^4, which is wrong. help please?

taking f(x) = 1/4x^4 - 4x^2 +25:
b. find values of x for which f'(x) = 0
got it right, answers are 0, 2 root 2, -2 root 2

c. hence or orhterwise find minimum distance from O to the curve, showing that your answer is a minimum.

11. curve with equation y= 3+5x+x^2-x^3. curve touches x axis at A and crosses x axis at C. Points A and B are stationary points on the curve.

a. show that C has coordinates (3,0)
b. using calculus and showing all working, find coordinates of A and B.
(answer= A (-1,0) B (5/3 , 9 13/27)

So I'd like help on 10a, c, and 11a, b.
Thank you soooo much!!!!
2. (Original post by BrownieLover)
[SIZE=4]Hi.

pg 152 of c2 Edexcel book,
the diagram shows the part of the curve with equation y=5-0.5x^2 for which y is greather than or equal to 0.
O is (0,0)
a. show that OP^2 = 1/4x^4 - 4x^2 +25

Didn't get this one right... i got x^2 + 25 -1/4x^4, which is wrong. help please?

]
You have incorrectly squared y

(a-b)^2 is NOT a^2 -b^2

You need to square the bracket
3. For part c

Second differential to find which is the minimum

Then put x into the correct equation for the length

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