Answer:
the answer is A,
P(x) = -0.4x³+100x²-900x+500
Step-by-step explanation:
monthly cost:
[tex]c(x) = 600x {}^{2} + 300x[/tex]
monthly revenue:
[tex]r(x) = - 0.4 {}^{3} + 700x {}^{2} - 600x + 500[/tex]
profit function:
[tex]p(x) = r(x) - c(x)[/tex]
[tex]p(x) = ( - 0.4x {}^{3} + 700 {x}^{2} - 600x + 500) - (600x {}^{2} + 300x)[/tex]
i) remove the first bracket
[tex]p(x) = - 0.4x {}^{3} + 700x {}^{2} - 600x + 500 - (600 {x}^{2} + 300x)[/tex]
ii) there is a negative sign, '-' in front of the second bracket. so, change the sign of each term of the expression inside the bracket
[tex]p(x) = - 0.4x {}^{3} + 700 {x}^{2} - 600x + 500 - 600x {}^{2} - 300x[/tex]
iii) collect like terms
[tex]p(x) = - 0.4x {}^{3} + 700 {x}^{2} - 600 {x}^{2} - 600x - 300x + 500[/tex]
iv) simply the like terms
[tex]p(x) = - 0. 4{x}^{3} + 100 {x}^{2} - 900x + 500 [/tex]
