y = (cos7x)^x lny = x(lncos7x) y/y' = (x ) 1/(cos7x) (-sin7x) + lncos7x y/y' = -xtan7x + lncos7x y' = ((cos7x)^x) (-xtan7x + lncos7x) Is this wrong? Why?
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$\displaystyle (cos(nx))' = -n \cdot sin(nx)$ You forgot the n the answer is $\displaystyle y' = (cos^x(7x)) \cdot (log(cos(7x)) - 7xtan(7x))$
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