theorem Th90: :: EUCLID_8:99

for r being Real
for f1, f2, f3 being PartFunc of REAL,REAL
for t0 being Real st f1 is_differentiable_in t0 & f2 is_differentiable_in t0 & f3 is_differentiable_in t0 holds
VFuncdiff ((r (#) f1),(r (#) f2),(r (#) f3),t0) = r * (VFuncdiff (f1,f2,f3,t0))