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.
Related Maths A Level answers
All answers ▸How should I aproach a connected rates of change question.
The rate of growth of a population of micro-organisms is modelled by the equation: dP/dt = 3t^2+6t, where P is the population size at time t hours. Given that P=100 at t=1, find P in terms of t.
The point P (4, –1) lies on the curve C with equation y = f( x ), x > 0, and f '(x) =x/2 - 6/√x + 3. Find the equation of the tangent to C at the point P , giving your answer in the form y = mx + c. Find f(x)
a curve is defined by y=2x^2 - 10x +7. point (3, -5) lies on this curve. find the equation of the normal to this curve