### Home > PC > Chapter 1 > Lesson 1.1.2 > Problem1-24

1-24.

Suppose $f\left(x\right) = 2x^{2} − 3$, find:

1. $f\left(4\right)$

Substitute $4$ for every $x$ in the function.

$f\left(4\right) = 2\left(4\right)^{2} − 3$

1. $f\left(−5\right)$

Use ( ) when substituting to avoid errors.

$f\left(−5\right) = 2\left(−5\right)^{2} − 3$

1. $f\left(3b\right)$

Follow the same steps for (b).

1. $f\left(a + 1\right)$

Do not forget the middle term when expanding $\left(a + 1\right)^{2}$.

$2a^{2} + 4a − 1$