Me . this is quadratics applications. show how you get the quadratics. you don't need to solve the question. just need to know how to get the quadratics. so much.

the cross section of an object is the shape you get when you cut straight through an object.

thus the cross section of the human hair is a circle. hence the cross sectional area is the area of a circle and area of circle is :

a = 3.14 × r²

we are given that the average width of human hair is = 4 × (1 / 10³) cm.

so the diameter of the circle is = 4 × (1 / 10³) cm.

∴ radius r = (diameter/2) = 2 × (1/10³) cm

now area a = 3.14 × (2 × (1/10³))² cm²

scientific notation is a standard way of writing very large and very small numbers so that they’re easier to both compare and use in computations. to write in scientific notation, follow the form

n × 10 ᵃ

where n is a number between 1 and 10, but not 10 itself, and a is an integer (positive or negative number).

so area can be rewritten in scientific notation as :

⇒ 3.14 × 4 × (1/10⁶)

⇒ 12.56 × 10 ⁻⁶ cm²

⇒1.256 × 10⁻⁷ cm²