Question

Can some one explain how to write functions

Answer 1

f(x)=2x+34 is a function

Answer 2

A function is a relation that pairs each input with one output. The input are your x-values and the output is your y-values. A relation is a set of ordered pairs so like {(1,1), (2,0),(3,2)}. An expression is not a function when it does not pass the vertical line test or if we have an input going to two different outputs. So, {(1,1), (1,2)(3,0)} is not a function since our input 1 goes to the two different outputs being 1 and 2. This is like saying F(1)= 1 or 2.
To write a function you could either write out different equations or write out a set of ordered pairs or use a diagram depending on what the question wants or your personal preference.

Answer 3

Note: this also depends on your independent and dependent variables. Like y=x^2 where y is the dependent variable and x is the independent variable, is a function but x=y^2 is not if our independent variable is still x and the dependent variable is y.