# How do you evaluate f(x)=2|-x+3|-9x for x=-4?

Mar 31, 2017

See explanation.

#### Explanation:

To calculate the value of an expression for a specified value of a variable you substitute the given value for all occurences of the variable and then simplify the expression:

$f \left(x\right) = 2 \times | - x + 3 | - 9 x$

So

$f \left(- 4\right) = 2 \times | - \left(- 4\right) + 3 | - 9 \cdot \left(- 4\right) = 2 \times | 4 + 3 | - 9 \cdot \left(- 4\right) =$
$= 2 \times | 7 | + 36 = 14 + 36 = 50$