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Let A (0,0) and B(8,2) be two fixed poin...

Let A (0,0) and B(8,2) be two fixed points on the curve `y^(3) =|x|` A point C (abscissa is less than 0) starts moving from origin along the curve such that rate of change in the ordinate is 2 cm/sec. After `t_(0)` seconds, triangle ABC becomes a right triangle.
After `t_(0)` secods, tangent is drawn to teh curve at point C to intersect it again at `(alpha,beta).` Then the value of `4alpha+3 beta` is

A

`4/3`

B

`3/4`

C

2

D

1

Text Solution

AI Generated Solution

The correct Answer is:
To solve the problem step by step, we will analyze the given information and apply the concepts of derivatives and geometry. ### Step 1: Understand the curve and the movement of point C The curve is given by the equation \( y^3 = |x| \). Since point C has an abscissa (x-coordinate) less than 0, we can rewrite the equation as: \[ y^3 = -x \] This implies: \[ x = -y^3 \] ### Step 2: Determine the relationship between x and y Since point C is moving along the curve, we can express the coordinates of point C as: \[ C(-y^3, y) \] where \( y \) is the ordinate (y-coordinate) of point C. ### Step 3: Find the rate of change of y We are given that the rate of change of the ordinate \( y \) is \( \frac{dy}{dt} = 2 \) cm/sec. ### Step 4: Differentiate the curve equation To find \( \frac{dx}{dt} \), we differentiate the equation \( y^3 = -x \) with respect to time \( t \): \[ \frac{d}{dt}(y^3) = \frac{d}{dt}(-x) \] Using the chain rule: \[ 3y^2 \frac{dy}{dt} = -\frac{dx}{dt} \] Substituting \( \frac{dy}{dt} = 2 \): \[ 3y^2 \cdot 2 = -\frac{dx}{dt} \] Thus, \[ \frac{dx}{dt} = -6y^2 \] ### Step 5: Find the coordinates of point C after \( t_0 \) seconds At \( t = t_0 \), the ordinate \( y \) can be expressed as: \[ y = 2t_0 \] Substituting this back into the equation for \( x \): \[ x = -y^3 = -(2t_0)^3 = -8t_0^3 \] So, the coordinates of point C are: \[ C(-8t_0^3, 2t_0) \] ### Step 6: Determine when triangle ABC is a right triangle For triangle ABC to be a right triangle, we can use the condition that the dot product of vectors AB and AC must be zero. The coordinates of points A and B are \( A(0,0) \) and \( B(8,2) \). The vectors are: \[ \overrightarrow{AB} = (8 - 0, 2 - 0) = (8, 2) \] \[ \overrightarrow{AC} = (-8t_0^3 - 0, 2t_0 - 0) = (-8t_0^3, 2t_0) \] The dot product is: \[ \overrightarrow{AB} \cdot \overrightarrow{AC} = 8(-8t_0^3) + 2(2t_0) = -64t_0^3 + 4t_0 \] Setting this equal to zero for the right triangle condition: \[ -64t_0^3 + 4t_0 = 0 \] Factoring out \( 4t_0 \): \[ 4t_0(-16t_0^2 + 1) = 0 \] This gives us: \[ t_0 = 0 \quad \text{or} \quad 16t_0^2 = 1 \Rightarrow t_0 = \frac{1}{4} \] ### Step 7: Find the tangent at point C Now, we need to find the tangent line at point C after \( t_0 \) seconds. The coordinates of C are: \[ C(-8(\frac{1}{4})^3, 2(\frac{1}{4})) = C(-\frac{1}{8}, \frac{1}{2}) \] The slope of the tangent line at C can be found using: \[ \frac{dy}{dx} = \frac{dx/dt}{dy/dt} = \frac{-6y^2}{2} = -3y^2 \] At \( y = \frac{1}{2} \): \[ \frac{dy}{dx} = -3\left(\frac{1}{2}\right)^2 = -\frac{3}{4} \] ### Step 8: Equation of the tangent line Using point-slope form: \[ y - \frac{1}{2} = -\frac{3}{4}\left(x + \frac{1}{8}\right) \] Simplifying this gives: \[ y = -\frac{3}{4}x - \frac{3}{32} + \frac{1}{2} = -\frac{3}{4}x + \frac{16 - 3}{32} = -\frac{3}{4}x + \frac{13}{32} \] ### Step 9: Find the intersection point (α, β) To find the intersection of the tangent line with the curve \( y^3 = -x \), substitute \( y = -\frac{3}{4}x + \frac{13}{32} \) into \( y^3 = -x \): Let \( y = \beta \): \[ \beta^3 = -\alpha \] Substituting \( \beta = -\frac{3}{4}\alpha + \frac{13}{32} \) into this equation and solving will yield the values of \( \alpha \) and \( \beta \). ### Step 10: Calculate \( 4\alpha + 3\beta \) After finding \( \alpha \) and \( \beta \), compute \( 4\alpha + 3\beta \).
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