In the periodic table of elements, what do all the elements 2 in a row have in common

What is the length x of the side of the triangle below? (hint: use the cosine function)

Which of the following are properties of mechanical waves? check all that apply ⭕️ particles of the medium move back and fourth, but do not move with the wave. ⭕️ the particles of the medium always move parallel to the wave motion. ⭕️ wave motion begins with a disturbance in the medium. ⭕️ waves transport energy from a source outward, away from the source.

The dot diagram represents the motion of the motorcycle as it moves from left to right