# Can someone explain why my graph is wrong? (sketching f(x) from f'(x))

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#1
Question (part d): http://prntscr.com/s97kn5

My diagram: http://prntscr.com/s97qmu

Diagram in textbook: http://prntscr.com/s97r0x
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11 months ago
#2
D is a negative cubic graph of f'(x) = -(x-2)(x+1)^2
so f(x) = −(x^4 - 6x^2 +8x)/4 + C
so your graph fits the pattern of being a negative quartic graph but I think your roots are wrong
Last edited by kubes_04; 11 months ago
0
11 months ago
#3
(Original post by kubes_04)
D is a negative cubic graph of f'(x) = -(x-2)(x+1)^2
so f(x) = −(x^4 - 6x^2 +8x)/4 + C
so your graph fits the pattern of being a negative quartic graph but I think your roots are wrong
f'(x) ~ -(x+2)(x-1)^2.
Looks like the book is wrong. From the very left f must be increasing as the gradient is positive.
If the book was -y, it would be similar to the OPs.
Last edited by mqb2766; 11 months ago
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11 months ago
#4
(Original post by TSR360)
Question (part d): http://prntscr.com/s97kn5

My diagram: http://prntscr.com/s97qmu

Diagram in textbook: http://prntscr.com/s97r0x
Diagram in textbook is wrong.

E.g. for x < -2 the gradient is +ve so the curve must be increasing, whereas their answer shows it decreasing.
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