Question

If f(x)=x^2 -2x-5 find the following values. a) f(2) b) f(4) c) f(-3)

Answer 1

a -5

b) 3

c) 10

Explanation:

`f(x) = x^2 - 2x - 5\\\\a) \;f(2) = (-2)^2-2(2) -5\\= 4 - 4 - 5 = -5\\\\`

`b) f(4) = 4^2 - 2(4) - 5 = 16 - 8 - 5 = 16 -13 =3`

`c) f(-3) = (-3)^2 - 2(-3) - 5 = 9 + 6 - 5 = 15-5 = 10 \\\mathrm {because\; (-2(-3) \;becomes\; +6}`

Answer 2

- 5, 3 and 10

Explanation:

(a)

substitute x = 2 into f(x)

f(2) = 2² - 2(2) - 5 = 4 - 4 - 5 = 0 - 5 = - 5

(b)

substitute x = 4 into f(x)

f(4) = 4² - 2(4) - 5 = 16 - 8 - 5 = 8 - 5 = 3

(c)

substitute x = - 3 into f(x)

f(- 3) = (- 3)² - 2(- 3) - 5 = 9 + 6 - 5 = 15 - 5 = 10