Which set of rectangular coordinates describes the same location as the polar coordinates [tex]\left(3 \sqrt{2}, \frac{3 \pi}{4}\right)[/tex]?

A. [tex](-3, 3)[/tex]
B. [tex](3, -3)[/tex]
C. [tex](-3 \sqrt{2}, 3 \sqrt{2})[/tex]
D. [tex](-3, -3)[/tex]



Answer :

To convert polar coordinates to rectangular coordinates, we have a given polar coordinate [tex]\((r, \theta)\)[/tex]. The formulas to convert these to rectangular coordinates [tex]\((x, y)\)[/tex] are:
[tex]\[ x = r \cos(\theta) \][/tex]
[tex]\[ y = r \sin(\theta) \][/tex]

Given the polar coordinates are:
[tex]\[ r = 3 \sqrt{2} \][/tex]
[tex]\[ \theta = \frac{3\pi}{4} \][/tex]

We need to find the values of [tex]\(x\)[/tex] and [tex]\(y\)[/tex] using the above formulas for [tex]\(r = 3 \sqrt{2}\)[/tex] and [tex]\(\theta = \frac{3\pi}{4}\)[/tex].

1. Calculate [tex]\(x\)[/tex]:
[tex]\[ x = r \cos(\theta) \][/tex]
Substitute the values of [tex]\(r\)[/tex] and [tex]\(\theta\)[/tex]:
[tex]\[ x = 3 \sqrt{2} \cdot \cos\left(\frac{3\pi}{4}\right) \][/tex]

We know the value of [tex]\(\cos\left(\frac{3\pi}{4}\right)\)[/tex] is [tex]\(-\frac{\sqrt{2}}{2}\)[/tex]:
[tex]\[ x = 3 \sqrt{2} \cdot -\frac{\sqrt{2}}{2} \][/tex]
[tex]\[ x = 3 \sqrt{2} \cdot -\frac{\sqrt{2}}{2} = -3 \][/tex]

2. Calculate [tex]\(y\)[/tex]:
[tex]\[ y = r \sin(\theta) \][/tex]
Substitute the values of [tex]\(r\)[/tex] and [tex]\(\theta\)[/tex]:
[tex]\[ y = 3 \sqrt{2} \cdot \sin\left(\frac{3\pi}{4}\right) \][/tex]

We know the value of [tex]\(\sin\left(\frac{3\pi}{4}\right)\)[/tex] is [tex]\(\frac{\sqrt{2}}{2}\)[/tex]:
[tex]\[ y = 3 \sqrt{2} \cdot \frac{\sqrt{2}}{2} \][/tex]
[tex]\[ y = 3 \sqrt{2} \cdot \frac{\sqrt{2}}{2} = 3 \][/tex]

Therefore, the corresponding rectangular coordinates are:
[tex]\[ (x, y) = (-3, 3) \][/tex]

So, the correct answer is:
A. [tex]\((-3, 3)\)[/tex]