Yahoo Answers is shutting down on May 4th, 2021 (Eastern Time) and beginning April 20th, 2021 (Eastern Time) the Yahoo Answers website will be in read-only mode. There will be no changes to other Yahoo properties or services, or your Yahoo account. You can find more information about the Yahoo Answers shutdown and how to download your data on this help page.
Trending News
can anyone help me with these differentiation problems?
1. Find a third-degree polynomial Q such that Q(1) = 1, Q '(1) = 3, Q ''(1) = 8, and Q '''(1) = 36
2. Find constants A, B, and C such that the function y = Ax2 + Bx + C satisfies the differential equation y '' + y ' - 2y = x2.
3 Answers
- Scott RLv 61 decade agoFavorite Answer
1)
let Q = ax^3 + bx^2 + cx + d
Q' = 3ax^2 + 2bx + c
Q'' = 6ax + 2b
Q''' = 6a
so Q'''(1) = 36
6a = 36
a = 6
Q''(1) = 8
6ax + 2b = 8
36 + 2b = 8
2b = -28
b = -14
Q'(1) = 3
3ax^2 + 2bx + c = 3
18 - 28 + c = 3
-10 + c = 3
c = 13
and Q(1) = 1
so ax^3 + bx^2 + cx + d = 1
or 6 - 14 + 13 + d = 1
5 + d = 1
d = -4
so Q = 6x^3 - 14x^2 + 13 x - 4
2)
y = Ax^2 + Bx + C
y' = 2Ax + B
y'' = 2A
so if y '' + y ' - 2y = x^2
2A + (2Ax + B) - 2(Ax^2 + Bx + C) = x^2
-2Ax^2 +(2A-2B)x + (2A +B - 2C) = x^2
Therefore,
-2A = 1 (since the coefficient of x^2 on the right hand side is 1)
or A = -1/2
2A - 2B = 0 (since there is no x term on the right hand side)
-1 - 2B = 0
b = -1/2
2A +B - 2C = 0 (since there is no constant term on r.h.s.)
-1 - 1/2 - 2C = 0
2C = -3/2
C = -3/4
- ?Lv 44 years ago
f(x) + x^2 * (f(x))^3 = 10 f'(x) + x^2 * 3 * (f(x))^2 * f'(x) + 2x * (f(x))^3 = 0 f(a million) = 2 f'(a million) + a million^2 * 3 * (2)^2 * f'(x) + 2 * a million * (2)^3 = 0 f'(a million) * (a million + 3 * 4) + 2 * 8 = 0 f'(a million) * 13 = -sixteen f'(a million) = -sixteen/13 All I used became into the product rule. enable f(x) = y y + x^2 * y^3 = 10 y' + x^2 * 3y^2 * y' + y^3 * 2x = 0 x = a million, y = 2 y' + a million * 12 * y' + 2^3 * 2 * a million = 0 y' * (a million + 12) = -sixteen y' = -sixteen/13 See? comparable element, with out the sensible notation
- santmann2002Lv 71 decade ago
y=ax^3+bx^2+cx+d
y'=3ax^2+2bx+c
y''= 6ax +2b
y'''=6a =36
a=6
36+2b=8 b= -12
18-24+c=3 c=9 a+b+c+d=1 6-12+9+d= 1 d=-2
Q(x) = 6x^3-12x^2+ 9x-2
2)y''=2A ,y'=2Ax+B y= Ax^2 +Bx +C
2A+2Ax+B -2Ax^2-2Bx-2C =x^2
-2A=1 A =-1/2 (-1-2B)= 0 B=-1/2
-1 -1/2 -2C= 0 C=-3/4