Answer:
The road width is x = 10 m.
Step-by-step explanation:
A formula for the area of the horizontal rectangle is A1 = (x)(20 m).
A formula for the small rectangle on top of that is A2 = (x)(18 - x).
The total area of the new roadway is 280 m^2.
Summing up A1 and A2 and equating the result to 280 m^2, we get:
20x + 18x - x^2 = 280
Rewriting this in the standard quadratic form:
-x^2 + 38x - 280 = 0
Here the coefficients are a = -1, b = 38 and c = -280.
The discriminant is thus b^2 - 4ac, or:
38^2 - 4(-1)(-280) = 1444 - 4(280) = 324, or 18^2.
Thus, the roots (x-values) are:
-38 ± 18
-------------- = 28 and 10
-2
Only the value x = 10 makes sense here, so we omit the other value (28).
The road width is x = 10 m.
x = ----------------------
