Answer
The slope of the second bird that flew perpendicular to the first bird was -2.
Work Step by Step
To determine the slope of second bird that flew to perpendicular to first bird, find the slope of the first bird. The perpendicular slope would be the negative reciprocal of the original slope.
First Bird
(1,2), (5,4)
Slope = $\frac{Rise}{Run}$ = $\frac{Y2-Y1}{X2-X1}$ = $\frac{4-2}{5-1}$ = $\frac{2}{4}$ = $\frac{1}{2}$
Slope of First bird = $\frac{1}{2}$
Slope of Second bird = -$(\frac{1}{2})^{-1}$ = -2
