If is a cube, we have: .
Then must be of the form: .
. . (Do you see why?)
The least value of occurs when
. . Hence: .
And we have: .
Therefore: . . . . answer (d)
I am stumped on this one.
Assume m and n are positive integers. 75m = n^3. What is the minimum possible value of m + n?
I was unsure of where to begin, so I tried to set up a system of equations and try each possible answer.
75m = n^3, m + n = 15
But, this gave me imaginary numbers when I tried solving each possible answer. I'm guessing that I'm going at this completely wrong.
I know that when you have a quadratic you can find the minimum by -b/2a when in the form y = ax^2 + bx + c, but I didn't think I could do this when I have a cube there.
Thanks for your reply. Is the reason m must be in that form because the 3's and 5's must be in groups of 3?
So, if the problem said 225m = n^3, then m would be in the form m = 3 * 5 * k^3?
Oh, and I did work it out with a system of equations, and it checked out. I guess I was just doing those wrong?