What is the limit, as x goes to 0, of [sinx(1-cosx)]/(2x^2)?

write it as

lim (1/2)(sinx/x)(1-cosx)/x
x ---> 0

you should have learned that
lim sinx/x = 1 and lim (1-cosx)x =0
so the above is

(1/2)(1)(0) = 0