作者:David Kedrowski 14 年以前
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The derivative is important to three of the four major problems that led to the development of calculus.
Taking derivatives of derivatives.
Position
Velocity
Acceleration
Jerk
We've been finding first derivatives.
The second derivative is the derivative of the first derivative.
The fifth derivative is the derivative of the fourth derivative.
d
---[ tan x ] = sec^2 x
dx
d
---[ cot x ] = -csc^2 x
dx
d
---[ sec x ] = sec x tan x
dx
d
---[ csc x ] = -csc x cot x
dx
The product f/g of two differentiable functions f and g is itself differentiable at all values of x for which g(x) is not zero. Moreover, the derivative of f/g is given by the denominator times the derivative of the numerator minus the numerator times the derivative of the denominator, all divided by the square of the denominator.
d f(x) g(x) f'(x) - f(x) g'(x)
---[ ---- ] = ------------------------, g(x)<>0
dx g(x) [g(x)]^2
The product of two differentiable functions f and g is itself differentiable. Moreover, the derivative of fg is the first function times the derivative of the second, plus the second function times the derivative of the first.
d
---[ f(x) g(x) ] = f(x) g'(x) + g(x) f'(x)
dx
Average velocity = secant line (no limit)
Instantaneous velocity = tangent line (limit)
Speed is the absolute value of velocity (velocity is a vector quantity).
d/dx[sin x] = cos x
d/dx[cos x] = -sin x
The sum (or difference) of two differentiable functions f and g is itself differentiable. Moreover, the derivative of f+g (or f-g) is the sum (or difference) of the derivatives of f and g.
If f is a differentiable function and c is a real number, then cf is also differentiable and d/dx[cf(x)]=cf'(x).
The derivative of a power function x^n is nx^{n-1} for n a rational number.
For f to be differentiable at x=0, n must be a number such that x^{n-1} is defined on an interval containing 0.
It is very useful to rewrite radicals into rational exponent form and to write variables in the denominator of a fraction in negative exponent form.
The derivative of x is 1.
This follows from the fact that the slope of the line y=x is 1.
The derivative of a constant function is 0.
This means that the slope of a constant function is 0.