Question

find the value of f(-9) and g(-2) if f(x)=-5x-2 and g(x)=3x^2-21x

Answer 1

Any ideas?

Answer 2

Replace the variable in the defining equation of the function by the given number and then simplify.

Answer 3

$$\Huge f(-9)=-5(-9)-2$$

Answer 4

Simplify that^ and try to do the second one on your own :-)

Answer 5

f(x) = -5x - 2 means there is a function in x called f which is defined as
y = -5x - 2.
The expression f(-9) means find the y value of function f when x = -9.
All you do is replace x with -9 in function f and evaluate the expression.

Then you are told about a function called g, and you are told what the function is.
Similarly, to find g(-2), you replace x with -2 in function g, and you evaluate the expression.

Answer 6

f(x) = -5x - 2 -> f(-9)=-5x-2
\[g(x)=3x^2-21x\] -> \[g(-2)=3x^2-21x\]

the new equations are f(-9)=-5x-2 and \[g(-2)=3x^2-21x\]. all you have to do is plug -9 in for the x's in the 1st equation and -2 in for the x's of the 2nd equation
f(-9)=-5x-2
f(-9)=-5(-9)-2
f(-9)=45-2
f(-9)=43

\[g(-2)=3x^2-21x\]
\[g(-2)=3(-2)^2-21(-2)\]
g(-2)=12+42
g(-2)=54