u seem to be new and hence ur knowledge is not enough to prove it 2 u(if u r not testing all of us)

but there r 3 ways by which i can help u

go for these if they seem to b helpful

1st

graph method

if u know graphs of both the curves i.e. y=sinx and y=x

then u can see that y=x is tangent to y= sinx at x=0

hence both of them have very close values at x=0

2nd

series mthod

sinx is just not a function but it is a series

sinx= x  - x^3/3! + x^5/5!....

so sinx/x= 1-x^2/3! + x^4/5!

hence wen we apply lim x tends to zero, sinx / x= 1

3rd

if u know L hopitals rule then u can prove it urself

all the best