3
f`(t)=20sin^42t*cos2t*2=40sin^42t*cos2t
f`(π/8)=40*sin^4π/4*cosπ/4=40*(1/√2)^4*√2/2=40*1/4*√2/2=5√2
4
f`(z)=e^sinz*cosz+e^cosz*(-sinz)
f`(π/2)=e^sinπ/2*cosπ/2-e^cosπ/2*sinπ/2=e*0-1*1=-1
5
f`(y)=1/tg3y*1/cos²3y*3=3cos3y/(sin3y*cos²3y)=6/sin6y
f`(π/12)=6/sinπ/2=6/1=6