Well,

you have x1 = 2 , y1 = 0 ..

By differentiating both sides w.r.t. x, we got:

solve for y' , then evaluate it at (2,0), i.e. when x=2 and y=0 to get the value of m ..

then substitute x1,y1 and m the tangent line's formula ..

Please, note that its called "tangent line's formula" not "tangent formula" ..