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Four points A(6,3) , B(-3,5) , C(4,-2) ...

Four points A(6,3) , B(-3,5) , C(4,-2) and D(x,2x) are given in such a way that `(" Area of " Delta DBC)/(" Area of " Delta ABC) = (1)/(2) ` The values of x is

A

` (5)/(6)`

B

` (2)/(3)`

C

` (11)/(6)`

D

` (8)/(3)`

Text Solution

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To solve the problem, we need to find the value of \( x \) such that the ratio of the area of triangle \( DBC \) to the area of triangle \( ABC \) is \( \frac{1}{2} \). ### Step 1: Calculate the Area of Triangle ABC The formula for the area of a triangle given vertices \( (x_1, y_1) \), \( (x_2, y_2) \), and \( (x_3, y_3) \) is: \[ \text{Area} = \frac{1}{2} \left| x_1(y_2 - y_3) + x_2(y_3 - y_1) + x_3(y_1 - y_2) \right| \] For triangle \( ABC \) with points \( A(6, 3) \), \( B(-3, 5) \), and \( C(4, -2) \): - \( x_1 = 6, y_1 = 3 \) - \( x_2 = -3, y_2 = 5 \) - \( x_3 = 4, y_3 = -2 \) Substituting these values into the area formula: \[ \text{Area}_{ABC} = \frac{1}{2} \left| 6(5 - (-2)) + (-3)(-2 - 3) + 4(3 - 5) \right| \] Calculating each term: 1. \( 6(5 + 2) = 6 \times 7 = 42 \) 2. \( -3(-2 - 3) = -3 \times -5 = 15 \) 3. \( 4(3 - 5) = 4 \times -2 = -8 \) Now, summing these: \[ \text{Area}_{ABC} = \frac{1}{2} \left| 42 + 15 - 8 \right| = \frac{1}{2} \left| 49 \right| = \frac{49}{2} \] ### Step 2: Calculate the Area of Triangle DBC For triangle \( DBC \) with point \( D(x, 2x) \), \( B(-3, 5) \), and \( C(4, -2) \): - \( x_1 = x, y_1 = 2x \) - \( x_2 = -3, y_2 = 5 \) - \( x_3 = 4, y_3 = -2 \) Substituting these values into the area formula: \[ \text{Area}_{DBC} = \frac{1}{2} \left| x(5 - (-2)) + (-3)(-2 - 2x) + 4(2x - 5) \right| \] Calculating each term: 1. \( x(5 + 2) = 7x \) 2. \( -3(-2 - 2x) = -3(-2 - 2x) = 6 + 6x \) 3. \( 4(2x - 5) = 8x - 20 \) Now, summing these: \[ \text{Area}_{DBC} = \frac{1}{2} \left| 7x + 6 + 6x + 8x - 20 \right| = \frac{1}{2} \left| 21x - 14 \right| \] ### Step 3: Set Up the Ratio According to the problem, we have: \[ \frac{\text{Area}_{DBC}}{\text{Area}_{ABC}} = \frac{1}{2} \] Substituting the areas we calculated: \[ \frac{\frac{1}{2} |21x - 14|}{\frac{49}{2}} = \frac{1}{2} \] This simplifies to: \[ \frac{|21x - 14|}{49} = \frac{1}{2} \] Cross-multiplying gives: \[ |21x - 14| = \frac{49}{2} \] ### Step 4: Solve the Absolute Value Equation This leads to two cases: 1. \( 21x - 14 = \frac{49}{2} \) 2. \( 21x - 14 = -\frac{49}{2} \) **Case 1:** \[ 21x - 14 = \frac{49}{2} \] \[ 21x = \frac{49}{2} + 14 = \frac{49}{2} + \frac{28}{2} = \frac{77}{2} \] \[ x = \frac{77}{42} = \frac{11}{6} \] **Case 2:** \[ 21x - 14 = -\frac{49}{2} \] \[ 21x = -\frac{49}{2} + 14 = -\frac{49}{2} + \frac{28}{2} = -\frac{21}{2} \] \[ x = -\frac{21}{42} = -\frac{1}{2} \] ### Final Solution The possible values of \( x \) are \( \frac{11}{6} \) and \( -\frac{1}{2} \).
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