contestada

Starting from 200 ft​ away, your friend skates toward you and then passes you. She skates at a constant speed of 20 ​ft/s. Her distance d from you in feet after t seconds is given by d=l200-20tl. At what times is she 140 ft from​ you?

Respuesta :

Differentiate d

[tex]\\ \sf\longmapsto \dfrac{d}{dx}200-20t[/tex]

[tex]\\ \sf\longmapsto 20t[/tex](Velocity)

Now

20t-140=0[/tex]

[tex]\\ \sf\longmapsto 20t=140[/tex]

[tex]\\ \sf\longmapsto t=\dfrac{140}{20}[/tex]

[tex]\\ \sf\longmapsto t=7s[/tex]