Hello!

y = f(x) = x^2 - 8x +9

f ' (x) = 2x-8

f ' (3) = 6 - 8 = - 2 = m   ......(a)

taking tangent line into consideration (3,-6)

y - y1 = f ' (m) (x - x1) ..............( formula)

y - (-6) = (-2) ( x - 3 )    (putting 2 in place of m)

y +6 = - 2 x + 6     [(-(-)) = +]

y = - 2 x

ALL THE BEST. Hope the answer was helpful.

Thank You