A. Find h'(x) and h"(x).
B. Show that h is monotonic (that is, that either h always increases or remains constant or h always decreases or remains constant).
C. Show that the x-coordinate(s) of the location(s) of the critical points are independent of a and b.
Please show work.
Update:Consider the function h(x)=a(-2x+1)^5-b, where a≠0 and b≠0 are constants?
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Answers & Comments
h = a (−2x+1)⁵ − b
A.
h' = a * 5(−2x+1)⁴ * −2 − 0
h' = −10a(−2x+1)⁴
h'' = −10a * 4(−2x+1)³ * −2
h'' = 80a(−2x+1)³
B.
h is monotonic if h' ≤ 0 for all x, or if h' ≥ 0
h' = −10a(−2x+1)⁴
For a < 0, −10a > 0 and (−2x+1)⁴ ≥ 0
Therefore, h' ≥ 0 for all x, and h is non-decreasing
For a > 0, −10a < 0 and (−2x+1)⁴ ≥ 0
Therefore, h' ≤ 0 for all x, and h is non-increasing
C.
Critical points occur where h' = 0
−10a(−2x+1)⁴ = 0, where a ≠ 0
(−2x+1)⁴ = 0
x = 1/2
The only critical point is at x = 1/2, which is independent of a or b.
I'll assume the 6 was supposed to be a b.
Use the chain rule, with u=-2x+1 to write:
h(x) = au^5 + b
dh/dx = dh/du * du/dx .... chain rule
h'(x) = 5au^4 * (-2) = -10au^4 = -10a(-2x + 1)^4
h"(x) = d(h')/du * du/dx = -40au^3 * (-2) = 80au^3 = 80a(-2x + 1)^3
For all x≠1/2, (-2x + 1) is nonzero and (-2x + 1)^4 is positive. The sign of h' is the same as the sign of -10a, always the same sign...opposite that of a. That makes h(x) monontonic. Increasing if a<0 or decreasing if a>0.
h(x) is defined and differentiable everywhere (it's a polynomial) so the only critical points are the zero-derivative type.
0 = h'(x) = -10a(-2x + 1)^4 clearly requires -2x+1 = 0, and x = 1/2 is the only critical point. That's independent of a and b.
h(x) = a(1-2x)⁵ + b
A.
h′(x) = 5a(1-2x)⁴(-2) = -10a(1-2x)⁴
h″(x) = -10a×4(1-2x)³(-2) = 80a(1-2x)³
B. h′(x) always remains negative or at the most becomes zero at x = 1/2, hence h(x) is monotonically decreasing.
C. For critical points, h′(x) = 0, x = 1/2 which is independent of a and b.
Now, 10 pts. pleeeeeeeeeeeeeeez!!!!
b is not used in the equation. Did you mean h(x) = a(-2x+1)⁵-b ?
h(x) = a(-2x+1)⁵-b
h'(x) = -10a(-2x+1)⁴
h"(x) = 80a(-2x+1)³
h' = -10a (1 - 2x)^4
h" = 80a (1 - 2x)^3