Find the equation of the tangent line to the circle x2+y2=20x^2 + y^2 = 20x2+y2=20 at the point (2,4)(2, 4)(2,4).
x+2y=10x + 2y = 10x+2y=10
2x+4y=202x + 4y = 202x+4y=20
x+4y=20x + 4y = 20x+4y=20
x+2y=20x + 2y = 20x+2y=20