✔ 最佳答案
1. g(x) = f(sinx) + f(cosx)
g'(x) = cosx f'(sinx) - sinx f'(cosx) (連鎖法則)
g'(90*) = cos90* f'(sin90*) - sin90* f'(cos90*)
= 0 - (1)f'(0)
= -2
2.a. y = x^3 - 2x^2 + 4
dy/dx = 3x^2 - 4x
C在P的切綫的斜率 = 3a^2 - 4a
設該切綫方程為
y = mx + c
m = (3a^2 - 4a)
所以,y = (3a^2 - 4a)x + c
代x = 1,y = 0
0 = (3a^2 - 4a)(1) + c
c = 4a - 3a^2
所以,y = (3a^2 - 4a)x + (4a - 3a^2)
由於切綫通過P(a , b)
代x = a,y = b
b = (3a^2 - 4a)a + (4a - 3a^2)
b = 3a^3 - 7a^2 + 4a
2009-10-30 07:30:26 補充:
b = 3a^3 - 7a^2 + 4a ... (1)
但P(a , b)又合乎C的方程
b = a^3 - 2a^2 + 4 ... (2)
(2) X 3 - (1):
0 = a^2 - 4a + 12
然後就可求得a與b的值