Question Details

The slope of tangent to the curve x = t² + 3t – 8, y = 2t² – 2t – 5 at the point (2, -1) is

Options

A

22/7

B

6/7

C

-6/7

D

-6

Correct Answer :

-6/7

Solution :

The correct option is -6/7.

Let's find the slope of the tangent to the given curve step-by-step.

The curve is defined parametrically by the equations:
x = t 2 + 3 t 8
and
y = 2 t 2 2 t 5

Step 1: Find the value of the parameter t at the given point (2, -1).
At the point of tangency, we have x = 2 and y = -1. We can set up the equations to solve for t:
t 2 + 3 t 8 = 2
t 2 + 3 t 10 = 0
Factoring this quadratic equation gives:
( t + 5 ) ( t 2 ) = 0
This yields two possible values for t: t = -5 or t = 2.

Now, let's verify which of these values satisfies the equation for y:
2 t 2 2 t 5 = 1
2 t 2 2 t 4 = 0
Dividing the entire equation by 2:
t 2 t 2 = 0
Factoring this quadratic equation gives:
( t 2 ) ( t + 1 ) = 0
This yields the possible values: t = 2 or t = -1.

The value of t that satisfies both coordinate conditions for the point (2, -1) is the common solution, which is t = 2.

Step 2: Find the derivatives of x and y with respect to t.
Differentiating x with respect to t:
d x d t = d d t ( t 2 + 3 t 8 ) = 2 t + 3
Differentiating y with respect to t:
d y d t = d d t ( 2 t 2 2 t 5 ) = 4 t 2

Step 3: Calculate the slope of the tangent dy/dx.
Using the chain rule for parametric equations, the slope of the tangent is:
d y d x = d y / d t d x / d t = 4 t 2 2 t + 3

Step 4: Evaluate the slope at t = 2.
Substitute t = 2 into the expression for the derivative:
( d y d x ) t = 2 = 4 ( 2 ) 2 2 ( 2 ) + 3 = 8 2 4 + 3 = 6 7

Comparing this with our options, we note that the correct answer is indeed -6/7, representing the slope of the curve at the point corresponding to the evaluated coordinate system parameters.

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