Euler's Formula: e$^$i t$=$cos t$+$i sin t which also leads to: cos t$=$e$^$i t$+$e$^-$i t$/2$ and sin t$=$e$^$i t$-$e$^-$i t$/2$ i Rewrite the following expressions using the above formulas: $[$ cos $(3$ x$)=$; cos $^2(3$ x$)=]$ Use the above expression to evaluate the following trig integral in terms of e and i$.$cos $^2(3$ x$)$ d x$=$ Now convert your answer back to a real solution using Euler's Formula. $$cos $^2(3$ x$)$ d x