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find the three cube roots of 1 and express tham in rectangular coordinates.

for this problem

find the inverse function of y = 7x + 3

can i use this website for help

http://www.analyzemath.com/inversefunction/Tutorials.html

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x + 2y + x = 0
3x - y - z = 5
5x - 2y - 3z = 12

-------------------------------------------------------------------------
i already know the rules:

RULES:
a1x + b1y + c1z = d1
a2x + b2y + c2z = d2
a3x + b3y + c3z = d3

where the determinant D =
| a1 b1 c1 |
| a2 b2 c2 |  = / 0
| a3 b3 c3 |

then

Dx =
| d1 b1 c1 |
| d2 b2 c2 |
| d3 b3 c3 |

Dy =
| a1 d1 c1 |
| a2 d2 c2 |
| a3 d3 c3 |

Dz =
| a1 b1 d1 |
| a2 b2 d2 |
| a3 b3 d3 |

x = Dx/D
y = Dy/D
z = Dz/D

---------------------------------------------------------------------
now i did ::::::>>

x + 2y + x = 0
3x - y - z = 5
5x - 2y - 3z = 12

i did but not finished please help!

| 1    2    1   |
| 3  -1   -1  |  = / what ? not zero right
| 5  -2   -3  |

Dx =
| 0     2     1  |
| 5   -1    -1  |
|12  -2    -3  |

Dy =
| 1   0     1 |
| 3   5   -1 |
| 5  12  -3 |

Dz =
| 1    2   0 |
| 3  -1   5 |
| 5  -2  12|

x = Dx/D
y = Dy/D
z = Dz/D

HELP

solve for x:

log   x = sqrt(log    x)
     9                   9

find the three cube roots of -7 + 5i and express the roots in polar coordinates

ok i got stuck

R = sqrt(-7^2 + 5^2)
R = 4.898979486
R = 4.90

tan(theta) = -7/5
theta = ..............what???next
i dont know how ot do the next part...what does theta equal to?