Proof by contradiction is a form of proof that establishes the truth or the validity of a proposition, by showing that assuming the proposition to be false leads to a contradiction. I googled this so it may not be correct
as you may already know, to get the inverse of any expression, we start off by doing a quick switcheroo on the variables, and then solve for "y".
![\bf \stackrel{f(x)}{y}=x^3-9\implies \stackrel{\textit{quick switcheroo}}{\underline{x}=\underline{y}^3-9}\implies x+9=y^3\implies \sqrt[3]{x+9}=\stackrel{f^{-1}(x)}{y}](https://tex.z-dn.net/?f=%5Cbf%20%5Cstackrel%7Bf%28x%29%7D%7By%7D%3Dx%5E3-9%5Cimplies%20%5Cstackrel%7B%5Ctextit%7Bquick%20switcheroo%7D%7D%7B%5Cunderline%7Bx%7D%3D%5Cunderline%7By%7D%5E3-9%7D%5Cimplies%20x%2B9%3Dy%5E3%5Cimplies%20%5Csqrt%5B3%5D%7Bx%2B9%7D%3D%5Cstackrel%7Bf%5E%7B-1%7D%28x%29%7D%7By%7D)
Answer:

Step-by-step explanation:
We have been given four choices out of which we need to select the choice which is trinomial.
Trinomial means polynomial having three terms.
A) c2 + c + 6
It has 3 terms.
B) c2 − 16
It has 2 terms.
C) −8c
It has 1 term.
D) c3 + 4c2 − 12c + 7
It has 4 terms.
We see that only choice A) has three terms.
Hence correct choice is 
6×7=42 so the number missing is 42
3rd place to the left of the decimal point is the hundreds place
so the number 4 represents 4 hundred