$$ Predict$/$Calculate Four waves are described by the following equations, in which all distances are measured in centimeters and all times are measured in seconds: yA $=10$ cos$13$x$-4$t$2$ yB $=10$ cos$15$x $+4$t$2$ yC $=20$ cos$1-10$x $+60$t$2$ yD $=20$ cos$1-4$x$-20$t$2($a$)$ Which of these waves travel in the $+$x direction? $($b$)$ Which of these waves travel in the $-$x direction? $($c$)$ Which wave has the highest frequency? $($d$)$ Which wave has the greatest wavelength? $($e$)$ Which wave has the greatest speed?