AP Calculus ABmediummcq1 pt

The curve x2+4y2=8x^2+4y^2=8 passes through the point (2,1)(2,1). An equation of the tangent line to the curve at this point is

A.y1=12(x2)y-1=\dfrac{1}{2}(x-2)
B.y1=2(x2)y-1=-2(x-2)
C.y1=12(x2)y-1=-\dfrac{1}{2}(x-2)
D.y1=(x2)y-1=-(x-2)

Explanation

Core Concept

Implicit differentiation gives 2x+8ydydx=02x+8y\frac{dy}{dx}=0, so dydx=x4y=12\frac{dy}{dx}=-\frac{x}{4y}=-\frac{1}{2} at (2,1)(2,1). Point-slope form gives y1=12(x2)y-1=-\frac{1}{2}(x-2).

Correct Answer

Cy1=12(x2)y-1=-\dfrac{1}{2}(x-2)

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