NCEA Level 2 Calculus Preparation - Question 2

Thanks to Rinesh Rattan for spotting my mistake

At the equation of tangent part

-7 = -16(1)+c
-7 = -16 + c
-7 + 16 = c
9 = c

Equation is y = -16x + 9

[thantzinsine]

Can you solve this for me pls? Queston1. A function f(x) has been differentiated to f ' (x) = 9x^2 - 8x = 5
( i ) Find the equation of f( x) given the point (2, 20) lies on the curve.
( ii ) Calculate the equation of the tangent to f( x ) at the point (2, 20) where the gradient function f ' ( x ) = 9x^2 - 8x + 5.

[gabriellaleigh]

why does the y value (-7) become positive when you substituted into the y=mx+c equation?