Question

The point (7, 3pi/4) in polar coordinates is how far from the x-axis?

I just do 7sin(135) right? I get 4.9.

Answer 1

Yup that would be right.
Although you might want a more specific answer...
\[\sin 135=\frac{ 1 }{ \sqrt2 }\]
So \[7 \times \frac{ 1 }{ \sqrt2 }=\frac{ 7 }{ \sqrt2 }\]

Answer 2

You could rationalize that if you wanted