Mark M. answered 02/15/21
Retired math prof. Calc 1, 2 and AP Calculus tutoring experience.
x2 +4y2 -4x -8y + 3 = 0
Differentiate implicitly with respect to x: 2x + 8y(dy/dx) - 4 - 8(dy/dx) = 0
dy/dx = (-2x + 4) / (8y - 8)
Slope of tangent line = dy/dx evaluated at the point (1,2) = 1/4
Equation of tangent line: y - 2 = (1/4)(x - 1)
y = (1/4)x + 7/4