If f(x)=x^2+5 and g(x)=5x+4 what is [fog](6)

Answer 1

The variable in the expression for f(x) should be replaced with g(x), as follows: ( )^2 +5.

This expression is (5x + 4)^2 + 5, which is 25x^2 + 40x + 16 + 5. Notice that the constant of 5 is STILL in the expression. Now simplify, by combining LIKE TERMS, to 25x^2 + 40x + 21. Therefore, f o g( x) = 25x^2 40x + 21. That's it!

Answer 2

When doing a function of a function always start with the function on the right

g(6)= 5(6) +4 = 34

f(34)= 34^2 +5= 1156 +4 = 1160