у'=(13tgx-13x+5)=13/cos^2x-13=13-13cos^2x/cos^2=13(1-cos^2x)/cos^2x=13tg^2x
[-п/4;0]
2)13tg^2x=0
tgx=0
x=0+Пn,nэZ
x=Пn
x=0
f(-п\4)=13*tg(-п/4)-13*(-п/4)+5=-13+13п/4+5=-8+13п/4
f(0)=13*tg(0)-13*0+5=5
