Area bounded by the straight lines $x^2y-y^3-x^2+5y^2-8y+4=0$ (in sq. units) is
Step-by-Step Solution
Key Concept: Factor: $(y-1)(x^2-y^2-4y+4)=(y-1)(x^2-(y-2)^2)=(y-1)(x-y+2)(x+y-2)$. These are lines $y=1$, $x=y-2$, $x=2-y$. Find triangle formed.
Step 1: Factorize the given equation to identify the constituent lines.
The given equation is $x^2y-y^3-x^2+5y^2-8y+4=0$.
We can group terms involving $x^2$:
$$x^2(y-1) - y^3 + 5y^2 - 8y + 4 = 0$$
Now, consider the polynomial in $y$: $P(y) = -y^3 + 5y^2 - 8y + 4$.
We test for integer roots. For $y=1$:
$$P(1) = -(1)^3 + 5(1)^2 - 8(1) + 4 = -1 + 5 - 8 + 4 = 0$$
Since $P(1)=0$, $(y-1)$ is a factor of $P(y)$. We can perform polynomial division or factor by grouping:
$$-y^3 + 5y^2 - 8y + 4 = -y^2(y-1) + 4y^2 - 8y + 4$$
$$= -y^2(y-1) + 4(y^2 - 2y + 1)$$
$$= -y^2(y-1) + 4(y-1)^2$$
$$= (y-1)(-y^2 + 4(y-1))$$
$$= (y-1)(-y^2 + 4y - 4)$$
$$= -(y-1)(y^2 - 4y + 4)$$
$$= -(y-1)(y-2)^2$$
Substitute this back into the main equation:
$$x^2(y-1) - (y-1)(y-2)^2 = 0$$
Factor out $(y-1)$:
$$(y-1)[x^2 - (y-2)^2] = 0$$
Step 2: Identify the equations of the straight lines.
The factored equation $(y-1)[x^2 - (y-2)^2] = 0$ implies that either $(y-1)=0$ or $[x^2 - (y-2)^2]=0$.
From $(y-1)=0$, we get the first line:
$$L_1: y=1$$
From $[x^2 - (y-2)^2]=0$, we can use the difference of squares formula $a^2-b^2=(a-b)(a+b)$:
$$(x - (y-2))(x + (y-2)) = 0$$
This gives two more lines:
$$(x - y + 2) = 0 \implies y = x+2 \quad (L_2)$$
$$(x + y - 2) = 0 \implies y = -x+2 \quad (L_3)$$
Thus, the given equation represents three straight lines: $y=1$, $y=x+2$, and $y=-x+2$.
Step 3: Determine the vertices of the region bounded by these lines.
The region is a triangle formed by the intersection of these three lines.
1. Intersection of $L_1$ and $L_2$: $y=1$ and $y=x+2$.
Substituting $y=1$ into $y=x+2$:
$1 = x+2 \implies x = -1$.
Vertex $A = (-1, 1)$.
2. Intersection of $L_1$ and $L_3$: $y=1$ and $y=-x+2$.
Substituting $y=1$ into $y=-x+2$:
$1 = -x+2 \implies x = 1$.
Vertex $B = (1, 1)$.
3. Intersection of $L_2$ and $L_3$: $y=x+2$ and $y=-x+2$.
Equating the expressions for $y$:
$x+2 = -x+2$
$2x = 0 \implies x=0$.
Substituting $x=0$ into $y=x+2$:
$y=0+2 \implies y=2$.
Vertex $C = (0, 2)$.
The vertices of the triangle are $A(-1, 1)$, $B(1, 1)$, and $C(0, 2)$.
Step 4: Calculate the area of the triangle.
We can use the base-height formula for the area of a triangle.
Consider the segment $AB$ as the base. $A(-1, 1)$ and $B(1, 1)$ lie on the line $y=1$.
The length of the base $AB$ is the distance between $x=-1$ and $x=1$ along $y=1$:
$$ \text{Base} = |1 - (-1)| = |2| = 2 \text{ units} $$
The height of the triangle is the perpendicular distance from vertex $C(0, 2)$ to the base line $y=1$.
The y-coordinate of $C$ is 2, and the y-coordinate of the base line is 1.
$$ \text{Height} = |2 - 1| = 1 \text{ unit} $$
The area of the triangle is given by:
$$ \text{Area} = \frac{1}{2} \times \text{Base} \times \text{Height} $$
$$ \text{Area} = \frac{1}{2} \times 2 \times 1 = 1 \text{ square unit} $$
The final answer is $\boxed{\text{1}}$.
Correct Answer: (A) 1