When x = 2, g(x) Let g(x) = 4x – 5. Find the indicated value

Question

I'm not sure how to do this is I could do the f(x)=-3+8 when x=5 I can do this but I don't know how to solve the g(x)

Answer 1

A function produces one (unique) result for each value of input.

 

Math often names the first variable x  (it could be anything, but we're stuck with habit).  The second variable is often called y, then z.  That's why the axes on a plot are labeled x and y (and z if it's 3D).

 

With word (story) problems, it is usually to choose names for variables that remind us (we're also forgetful) of what each variable means (that's called mnemonic).  For example, use N for the number of nickels and D for the number of dimes.  This works pretty well (like the 2-letter postal abbreviations for each state) until two of the variables have the same name.  Then, we have to have a rule (that we can remember, too) for remembering them.

 

All that to say, in math, when there already is a function named f(x), we have to use another name, and g(x) is often chosen.  It is a function and means exactly the same thing.   So f(x) and g(x) produce the same answer if the expressions defining them (on the right hand side) are also the same.

 

Hey, you said you can do that !

 

So, I'm curious --

     f(x) = -3+8   seems to ALWAYS result in 5 for every integer x    (did you make a typo? -- math and computers are very intolerant !)

 

Just plug x=2 into g(2) = 4(2) - 5       and feel very confident that you can do this, too.

Answer 2

Have a look at the answer I gave Brett on a very similar problem about an hour ago.  It explains what this is all about.