$(3$ pts$)1$a$)$ Briefly explain what is wrong with the following attempt to evaluate the integral ${\displaystyle \underset{0}{\overset{}{}}}co{s}^{3}xdx$

Use the Power Rule

${\displaystyle \underset{0}{\overset{}{}}}co{s}^{3}xdx$

$=\frac{1}{4}co{s}^{4}x{|}_x||=0^x=$

$=(\frac{1}{4}co{s}^4())-(\frac{1}{4}co{s}^4(0))$

$=(\frac{1}{4}(-1{)}^4)-(\frac{1}{4}(1{)}^4)$

$=\frac{1}{4}-\frac{1}{4}$

$=0$