please tolong dijawab kk beserta caranya

1. Turunin aja.
T^3-9/2 t^2-12t+5 = 0
Turunin lagi
3t^2 -9t -12 = 0
T^2 - 3t -4 =0
(T-4)(t+1)=0
So t = 4

2. Cari gradien gr singgung dulu
M = y'
Y' = sec^2(x)
Masukin π/4
(Sec π/4)^2= 2

So m2 = -1/2
Cari y= tan π/4 = 1
(π/4,1)
Y = mx + c
Y = -1/2 x +c
1 = -1/2 (π/4) + c
C = 1+π/8
So
Y = -1/2 x +1+π/8