Question 1021421: Write the equation -2x + 6y = 9 in polar form.
9sqrt(10)/20 = r cos (theta - 108)
9sqrt(10)/20 = r cos (theta - 72)
7sqrt(10)/20 = r cos (theta - 108)
7sqrt(10)/20 = r cos (theta - 72)
I'm really stuck here so any help would be very much appreciated, thanks!
Answer by rothauserc(4718)   (Show Source):
You can put this solution on YOUR website! -2x +6y = 9
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standard form is
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-2x +6y -9 = 0 then
2x -6y +9 = 0
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A=2, B=-6, C=9
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+ or - square root(4+36) = + or - 2square root(10)
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use -2square root(10), the minus is opposite sign of C
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(2x /(-2square root(10)) -6y/(-2square root(10)) +(9 / (-2square root(10)) = 0
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multiply the numerator and denominator of each fraction by square root(10)
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(-2square root(10) / 20)x +(6square root(10) / 20)y -(9square root(10) / 20) = 0
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note that -cos, +sin implies quadrant II
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phi = cos^(-1) of (-2square root(10) / 20) = 108.434948822
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correct answer is
(9 * square root(10) / 20) = r * cos(theta - 108)
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note that * means multiply
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