**A mapping f:R->R which id defined as f(x)=cosx; x in R is
a)one and one only b)onto only c)one one onto d)neither one one nor onto ?**

**Answer:**

The answer is b). A function like cosine is “onto” (aka surjective) because there are multiple inputs that provide the same output (i.e. 0 and 2pi are both 1).