Given x(t)=2(t−sin(t)) and y(t)=2(1−cos(t)), show the cycloid is concave down.
Find dtdx=2−2cos(t) and dtdy=2sin(t). 2. Find dxdy=1−cos(t)sin(t). 3. Find dx2d2y=2(1−cos(t))2−1. 4. Since the second derivative is always negative, the cycloid is always concave down.
How do you simplify (1−cos(t))2cos(t)(1−cos(t))−(sin(t))(sin(t))?
Expand: (1−cos(t))2cos(t)−cos2(t)−sin2(t). 2. Use sin2(t)+cos2(t)=1: (1−cos(t))2cos(t)−1. 3. Simplify: 1−cos(t)−1.
What is the first step in finding the second derivative of x=cos(t), y=sin(t)?
Find the first derivatives: dtdx=−sin(t) and dtdy=cos(t).
How do you find the slope of the tangent line to a parametric curve at a specific t?
Find dxdy=dx/dtdy/dt. 2. Evaluate dxdy at the given value of t.
How do you find the t-values where a parametric curve has a horizontal tangent?
Find dtdy. 2. Set dtdy=0 and solve for t. 3. Ensure dtdx is not also zero at those t-values.
How do you find the t-values where a parametric curve has a vertical tangent?
Find dtdx. 2. Set dtdx=0 and solve for t. 3. Ensure dtdy is not also zero at those t-values.
Difference between finding dxdy and dx2d2y for parametric equations?
dxdy: Find dx/dtdy/dt. dx2d2y: Find the derivative of dxdy with respect to t, then divide by dtdx.
Concave up vs. concave down: second derivative sign?
Concave up: second derivative > 0. Concave down: second derivative < 0.
First derivative vs. second derivative: what do they tell us?
First derivative: slope of the tangent line. Second derivative: concavity.
Parametric equations vs. standard equations: how to find derivatives?
Parametric: use dx/dtdy/dt. Standard: direct differentiation with respect to x.
Finding horizontal vs. vertical tangents in parametric equations?
Horizontal: set dtdy=0. Vertical: set dtdx=0.
Quotient rule vs. chain rule: when to use them?
Quotient rule: derivative of a ratio. Chain rule: derivative of a composite function.
dxdy vs dydx
dxdy is the rate of change of y with respect to x, while dydx is the rate of change of x with respect to y. They are reciprocals of each other.
First derivative test vs. second derivative test
First derivative test: finds local max/min using sign changes of f'(x). Second derivative test: uses the sign of f''(x) to determine concavity and local extrema.
Explicit vs. implicit differentiation
Explicit: y is directly defined as a function of x (y = f(x)). Implicit: y is defined implicitly in terms of x (e.g., x^2 + y^2 = 1).
Local vs. global extrema
Local: max/min within a specific interval. Global: absolute max/min over the entire domain.
Formula for dx2d2y in parametric form?
dx2d2y=dtdxdtd(dxdy)
How to find dxdy given x(t) and y(t)?
dxdy=dx/dtdy/dt
What is the trigonometric identity for sin2(t)+cos2(t)?
sin2(t)+cos2(t)=1
Formula for the derivative of a quotient vu?
dxd(vu)=v2v(dxdu)−u(dxdv)
Given x(t) and y(t), how to find the slope of the tangent line?
Calculate dxdy=dx/dtdy/dt and evaluate at the given t.
What is the formula for dx/dt if x(t)=2(t−sin(t))?
dtdx=2−2cos(t)
What is the formula for dy/dt if y(t)=2(1−cos(t))?
dtdy=2sin(t)
What is the formula for dtd(3(t−1)2)?
dtd(3(t−1)2)=−3(t−1)22
If dxdy=34t, what is dtd(dxdy)?
dtd(dxdy)=34
What is the formula for the second derivative of x=t3 and y=t4?