if f(x)=x^2+6x, find f(x+3)?

f(x+3)=(x+3)^2+6(x+3)
=x^2+6x+9+6x+18
=x^2+12x+27 answer//

f(x ) = x^2 + 6x
f(x+3)
= (x+3)^2 + 6(x+3)
= x^2 + 6x + 9 + 6x + 18
= x^2 + 12x + 27

f(x) = x^2 + 6x
f(x + 3) = (x + 3)^2 + 6(x + 3)
f(x + 3) = (x + 3)[(x + 3) + 6)]
f(x + 3) = (x + 3)(x + 3 + 6)
f(x + 3) = (x + 3)(x + 9)

Just plug in (x + 3) into every x you see in the function.

From f(x) --> f(x + 3):

f(x + 3) = (x + 3) ^ 2 + 6(x + 3)

Simplifying,

f(x + 3) = x ^ 2 + 6x + 9 + 6x + 18

or

f(x + 3) = x ^ 2 + 12x + 27

f(5) would be found by substituting x = 5 into x^2 + 6x.

In the same way, f(x + 3) is found by substituting (x + 3) for x:

f(x + 3) = (x + 3)^2 + 6(x + 3)

= x^2 + 6x + 9 + 6x + 18

= x^2 + 12x + 27

f(x + 3) = (x + 3)^2 + 6(x + 3)

It's not too hard. ;-)