hi every one i need help

Find the unit tangent vector at the indicated point of the vector

functionr(t) = e^15t cost i+e^15t sint j+e^15t k

T(pi/2) =

i compute the r'(t) = (-e^15tsint+15e^15tcost)i+(e^15tcost+15e^15tsint)j+( 15te^15t)k

now i need the norm of r'(t) which i coudn't find

plz help ??!!