Answer:
[tex] \sqrt{ {28x}^{2} - 6x } [/tex]
Step-by-step explanation:
You would substitute "2x" for every "x" in the function in the same way you would substitute any other number.
So if f(x)=Sqrt[7x²-3x], then: f(2x)=Sqrt[7(2x)²-3(2x)]
=Sqrt[7(4x²)-3(2x)]
=Sqrt[28x²-6x]
