The vertices of triangle ABC are A(2,3), B(–1,2), and C(3,1). If ΔDEF ∼ ΔABC and DE = 4AB, what is the length of EF? √10

If the length is 4 times from DE=4AB then the corresponding length of EF which is BC is also 4 times larger. Length of BC=sqrt((2-1)^2+(-1-3)^2)=sqrt of 17 Hence, length of EF is 1/4 of sqrt 17. Hope it helps