A student claims that the rectangular point below can be represented by the
polar coordinates (6√2,7π/4) and the polar coordinates (-6√2, 3π/7).

Is the student correct? Justify your answer using mathematics.

Since we don't have a figure we'll assume one of them is right and we're just being asked to check if they're the same number.  I like writing polar coordinates with a P in front to remind me.

It's surely false if that's really a 3π/7; I'll guess that's a typo that's really 3π/4.

P(6√2, 7π/4) = ( 6√2 cos 7π/4, 6√2 sin 7π/4 )

P(-6√2, 3π/4) = ( -6√2 cos 3π/4, -6√2 sin 3π/4 )

That's true since when we add pi to an angle it negates both the sine and the cosine,

cos(7π/4) = cos(π + 3π/4) = -cos(3π/4)

sin(7π/4) = sin(π + 3π/4) = -sin(3π/4)

TRUE