Question

If a= (4,-5) and b= (7,-9), what is the length of ab

Answer 1

The answer is 5 units.

Answer 2

A (4,-5)
B (7,-9)

$AB= \sqrt{(x_A-x_B)^2+(y_A-y_B)^2} \\ x_A=4; \ \ x_B=7; \ \ y_A=-5; \ \ y_B=-9; \\ \\ AB= \sqrt{(4-7)^2+(-5-(-9))^2}= \sqrt{(-3)^2+4^2} = \sqrt{25}=5$