3.27 walpole

The time to failure in hours of an important piece of electronic equipment used in a manufactured DVD player has the density function

f(x) = 1/2000 exp (-x/2000), x>=0

0, x<0

find F(x).

my queries :

- so meaning integrate from0 to xor 0 to infinity ?

- and could i use du=-x/2000 dx to solve ? i saw some of my mates using dt. which i don't know how does dt fit in .