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If a+b+c=0 then the family of lines 3ax+...

If `a+b+c=0` then the family of lines `3ax+by+2c=0` passes through the fixed point
(i) `(-2,(2)/(3))`
(ii) `(2,(3)/(3))`
(iii) `(2/3,2)`
(iv) none of these

A

`(-2,(2)/(3))`

B

`(2,(3)/(3))`

C

`(2/3,2)`

D

none of these

Text Solution

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The correct Answer is:
To determine if the family of lines given by the equation \(3ax + by + 2c = 0\) passes through the fixed points when \(a + b + c = 0\), we will follow these steps: ### Step 1: Substitute \(c\) in terms of \(a\) and \(b\) Given the equation \(a + b + c = 0\), we can express \(c\) as: \[ c = -a - b \] ### Step 2: Substitute \(c\) into the line equation Now, substituting \(c\) into the line equation \(3ax + by + 2c = 0\): \[ 3ax + by + 2(-a - b) = 0 \] This simplifies to: \[ 3ax + by - 2a - 2b = 0 \] ### Step 3: Rearranging the equation Rearranging the equation gives: \[ 3ax + by = 2a + 2b \] ### Step 4: Expressing the line in slope-intercept form We can express this in the form of \(y = mx + c\) (slope-intercept form): \[ by = -3ax + 2a + 2b \] Dividing through by \(b\) (assuming \(b \neq 0\)): \[ y = -\frac{3a}{b}x + \frac{2a}{b} + 2 \] ### Step 5: Finding the fixed point To find the fixed point, we can analyze the intercepts. The equation can be rewritten as: \[ 3x - 2 + \frac{b}{a}(y - 2) = 0 \] This indicates that the line passes through the point \((\frac{2}{3}, 2)\). ### Step 6: Checking the options Now, we will check the given options to see if any of them match the point \((\frac{2}{3}, 2)\): - (i) \((-2, \frac{2}{3})\) - (ii) \((2, 1)\) - (iii) \((\frac{2}{3}, 2)\) - (iv) none of these From our analysis, we see that option (iii) \((\frac{2}{3}, 2)\) is indeed the point through which the family of lines passes. ### Conclusion Thus, the correct answer is: \[ \text{(iii) } \left(\frac{2}{3}, 2\right) \]
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