Could someone please help me get started on this question. I seriously have no clue how to do part (i).
Given that y=mx + b is a tangent to the circle x^2 + y^2 = a^2.
(i) Show that b^2 = a^2 (m^2 +1)
(ii) If y = 3x + b and x^2 + y^2 = 25, find b.