PLEASE HELP

A pendulum is swinging back and forth. After t seconds, the horizontal distance from the bob to the place where it was released is given by H(t)=7−7cos( 2π(t−2)/20). How often does the bob cross its midline? Give an exact answer.

X/y + 4y/x divided by x/y - 2y/x explain as in depth as you can how you simplfied the fractions. i don't know where to start on this : /

The figure shows triangle def and line segment bc, which is parallel to ef: triangle def has a point b on side de and point c on side df. the line bc is parallel to the line ef. part a: is triangle def similar to triangle dbc? explain using what you know about triangle similarity. part b: which line segment on triangle dbc corresponds to line segment ef? explain your answer. part c: which angle on triangle dbc corresponds to angle f? explain your answer. asap

I’m really confused and need to learn this