The area of a rectangle is base * altitude, and the perimeter is 2*base + 2*altitude,
base = 10cm and altitude = 7cm
Start with the general formula. The key word is difference. So the general formula is
D(x) = W(x) - R(x) Now substitute in the values for W(x) and R(x)
D(x) = 0.002x^3 - 0.01x^2 - (x^2 - 4x + 13) Be very careful about the sign in front of the brackets.
D(x) = 0.002x^3 - 0.01x^2 - x^2 + 4x - 13 Do you see what that minus sign did? It affected all 3 terms.
D(x) = 0.002x^3 - 1.01x^2 + 4x - 13 <em>Note: -0.01 - 1x^2 = - 1.01 x^2</em>
That gives you a clear cut answer
C<<<<< answer.
That sign is the worst part of the question. Make sure you understand what it did.
A problem with extra information will be difficult to solve because you may not be able to tell what information you might need to use for the problem.
