How do you write a rational function that has the following properties: a zero at x= 4, a hole at x= 7, a vertical asymptote at x= -3, a horizontal asymptote at y= 2/5?

1 Answer
Jan 31, 2018

Rational function is (2x^2-22x+56)/(5x^2-20x-105)

Explanation:

A zero at x=4 means we have (x-4) as a factor in numerator;

a hole at x=7 means, we have x-7 a factor both in numerator as well as denominator;

a vertical asymptote at x=-3 means x+3 a factor in denominator only

a horizontal asymptote at y=2/5 means highesr degrees in both numerator and denominator are equal and their coefficients are in ratio of 2:5

Hence desired rational function is (2(x-4)(x-7))/(5(x-7)(x+3))

i.e. (2x^2-22x+56)/(5x^2-20x-105)

See its graph down below. Observe vertical asymptote x=-3 and horizontal asymptote y=2/5. We have a zero at x=4 as functtion passes through (4,0). Hole is not seen as x-7 cancels out, but we know, the function is not definedat this point.

graph{(2x^2-22x+56)/(5x^2-20x-105) [-10.67, 9.33, -4.4, 5.6]} 1