Evaluate gf(-5) for the functions f(x)=3x+7, g(x)=3x^2+6x-9
I like to think of gf(-5) as g ( f(-5) ), which helps visualise the order in which you need to calculate the output for each function. First you need to find the answer for f(-5), which you then use as the input for function g.
This gives: f(-5)= -53 +7= -15+7= -8Then using -8 as the input function g you get: g(-8)= 3(-8)^2+ 6*(-8) -9= 3*64-48-9= 192-48-9= 135
You don't need to do the entire equation at once, it's fine to find the answer for f(-5) and then g(-8) like I've shown, which for me makes it harder for me to put the wrong numbers in the wrong place. If you switch around the order that you do the functions you won't come to the correct answer so be careful when reading the question.
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