Answer:
The answer is below
Step-by-step explanation:
The question is not complete, the complete question is:
A rectangle is constructed with its base on the x-axis and two of its vertices on the parabola y 81-x², what are the dimensions of the rectangle with the maximum area? what is the area?
Solution:
Given the parabola:
y = 81 - x²
Let the points (a,0) and (-a, 0) be points on the axis, this points touch the parabola at (a, 81 - a²) and (-a, 81 - a²).
Points (a,0), (-a, 0), (a, 81 - a²), (-a, 81 - a²) form the rectangle.
The length of rectangle = distance between (a,0) and (-a, 0) or between (a, 81 - a²) and (-a, 81 - a²) = 2a
The breadth of rectangle = distance between (a,0) and (a, 81 - a²) or between (-a, 0) and (-a, 81 - a²) = 81 - a²
Area of rectangle (A) = length × breadth = 2a × (81 - a²) = 162a - 2a³
A = 162a - 2a³
The maximum area is at dA / da = 0
dA / da = 162 - 8a² = 0
162 - 6a² = 0
6a² = 162
a² = 27
a = 5.2 units
Length = 2a = 2(5.2) = 10.4 units
Breadth = 81 - a² = 81 - 5.2² = 54 unit
Area = length × breadth = 54 × 10.4 = 561 unit²
