Find the equation of a TANGENT line & NORMAL line to the curve of x^2+y^2=20such that the tangent line is parallel to the line 7.5x – 15y + 21 = 0

Answer 1

you want a tangent line with slope = 1/2
x^2+y^2 = 20
2x + 2yy' = 0
y' = -x/y
For the tangent line, you want a point on the circle where y = -2x
for the normal, you want 2y = x