Ill give brainliest pls !

how are electromagnetic waves different from mechanical waves?

select one:
a. electromagnetic waves are all high frequency; mechanical waves are all low frequency.
b. electromagnetic waves can travel through a vacuum; mechanical waves require a medium.
c. electromagnetic waves are visible; mechanical waves are invisible.
d. electromagnetic waves always reflect; mechanical waves always refract.

A is the correct answer..hope this helps

Explanation:Mechanical waves and electromagnetic waves are two important ways that energy is ... Matter that waves are traveling through is called a medium. ... The unit of frequency of a radio wave  one cycle per second

a and c

explanation:

both a and c are correct answers to my knowledge, it's been a bit since i've done anything related to magnetic fields, but it should be right.

i think it because equal matrices have equal dimensions, only square matrices can be symmetric. for all indices and . every square diagonal matrix is symmetric, since all off-diagonal elements are zero. in linear algebra, a real symmetric matrix represents a self-adjoint operator over a real inner product space.