Question

For y = 3x - 2x^2 +5x^3
show how to find the value for y, when x = 3. Show your work

Answer 1

y=3(3)-2(3)^2+5(3)^3
y=9-2(3)^2+5(3)^3
y=9-6^2+5(3)^3
y=9-36+5(3)^3
y=9-36+15^3
y=9-36+3,375
y=-27+3,375
y=3,348




Just do the steps as I showed you. Just go little by little for each thing so that you don't mess up our get super confused.

Answer 2

`y \: = \: f(x) \: = \: 3x \: - \: 2 {x}^(2) \: + \: 5 {x}^(3)`
Here, y is a cubic function of x.
When x = 3,

`y \: = \: f(3) \: = \: 3(3) \: - \: 2 {(3)}^(2) \: + \: 5 {(3)}^(3)`

`y \: = \: 9 \: - \: 18 \: + \: 135`

`y \: = \: f(3) \: = \: 126`
Hence, when x = 3, y = 126.