Natalie asked the following:
could you please show how to work out this question:
stuck on part (b)
Thanks for this, Natalie! Let's firstly check you did part (a) right.
f(x) is a function - literally a set of instructions of what to do to the value x.
So if the function f(x) is to do 7-4x, then any value of x can be operated on.
f(-2) means "do the function to x when x=-2"
So f(-2) = 7 - 4 (-2) = 7 + 8 = 15
Now to (b).
f(t) means let x=t (t is just another unknown number!)
The difference here is that we know what the function did to the number t: it gave the answer 9
So f(t) = 9 means that f(t) = 7 - 4t (i.e. you just need to set x=t)
But we know that f(t) = 9 so 7 - 4t = 9 is true.
So 7 = 9 + 4t
I hope this is clear! Good luck!