Answer:
(b) 10; 150°
Explanation:
You want the polar coordinate equivalent of (-5√3, -5).
Conversion
The polar form of (a, b) is ...
(a, b) = (r; θ)
where ...
r = √(a² +b²)
θ = arctan(b/a) . . . . . with attention paid to quadrant
Application
For the given values, the polar form is ...
r = √((-5√3)² +5²) = √(75 +25) = 10
θ = arctan(5/(-5√3)) = arctan(-1/√3) = 150°
The angle is a quadrant II angle with a reference angle of 30°.
The polar form is (10; 150°).
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Additional comment
Some calculators will do the coordinate conversion based on a vector or ordered pair. Others require the coordinates of the point to be expressed as a complex number, as in the attachment. (Note the calculator mode is set to DEGrees.)