Mark M. answered 06/15/15
Tutor
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Retired math prof. Calc 1, 2 and AP Calculus tutoring experience.
y = (sint)5t
To find y' (i.e., dy/dt) use logarithmic differentiation.
lny = 5t ln(sint)
y'/y = 5 ln(sint) + 5t (cost/sint)
y' = y[5 ln(sint) + 5t cot t] = (sin t)5t[ 5 ln(sint) + 5t cot t]