First, determine the slope of the tangent line. Take note that the slope of a line tangent to the curve is equal to the derivative of the function at the point of tangency. So taking the derivative of the function, f'(x) will be:
f'(x) = d/dx (x^3)
f'(x) = 3x^2
The given point of tangency is (1,1). Plugging in x=1 to the derivative yields:
f'(1) = 3(1)^2
f'(1) = 3
Hence, the slope of the line tangent to the function at (1,1) is m = 3.
Then, apply the point slope-form to get the equation of the tangent line.
y - y_1 =m(x - x_1)
y - 1 = 3(x - 1)
Isolating the y, it becomes:
y - 1 =3x - 3
y = 3x - 2
Thus, the equation of the tangent line is y = 3x - 2 .
Then, determine the intersection points of y = x^3 and y = 3x - 2. To do so, set the two y's equal to each other.
y = y
x^3 = 3x - 2
Take note that to solve polynomial equation, one side should be zero.
x^3 - 3x + 2 = 0
Then factor the left side using grouping method.
x^3 - x - 2x + 2=0
(x^3 - x) + (-2x + 2) = 0
x(x^2 - 1) - 2(x - 1) = 0
x(x-1)(x+1) - 2(x - 1) = 0
(x - 1)[x(x + 1) - 2] = 0
(x - 1)(x^2+x-2)=0
(x - 1)(x-1)(x + 2)=0
(x-1)^2(x + 2) = 0
Set each factor equal to zero.
(x-1)^2 = 0
x - 1=0
x=1
x + 2=0
x=-2
Then, plug-in the x values to either y=x^3 or y = 3x - 2, to get the y coordinates of the intersection.
x=1
y = 1^3=1
x=-2
y=(-2)^3 = -8
So, the two equations intersect at (1,1) and (-2,-8). Hence, bounded region of y = x^3 and y = 3x - 2 is:
To determine the area of the bounded region, draw a vertical strip. (See attached image.)
In the figure, the top of the vertical strip touches the graph of y=x^3. And its lower end touches the graph of y = 3x-2. Also, the bounded region starts at x=-2 and ends at x=1.
Applying the formula
A = int_a^b (y_(_(upper)) - y_(_(lower)))dx
the integral needed to compute the area of the bounded region is:
A = int_(-2)^1 (x^3-(3x-2))dx
Evaluating the integral, it results to:
A = int_(-2)^1 (x^3 -3x + 2)dx
A = (x^4/4 - (3x^2)/2+2x) |_(-2)^1
A = (1^4/4 - (3*1^2)/2+2*1) - ((-2)^4/4- (3*(-2)^2)/2+2*(-2))
A =3/4-(-6)
A=27/4
Therefore, the area of the bounded region is 27/4 square units.
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