If f(x) =2x+3 and f (2x+3) =5x , what is the value of 3x^2?

Answer 1

f(x) =2x + 3

then, if we plug "2x+3" in for x in the above equation, we would have 2(2x+3) + 3 but they tell us that f(2x+3) must equal 5x, so:

2(2x+3) + 3 = 5x

solving for x:

4x + 6 + 3 = 5x

9 = x

Plug that value into 3x² to get 3(9)² = 3(81) = 243