So I'm assuming that you're taking Calculus.
The first thing you want to do is take the integral of f(x)...
Use the power rule to get:
4X^2-13X+3.
Now solve for X when f(x)=0. This is because when the slope is 0, it is either a minimum or a maximum(I'm assuming you know this)
Now you get X=0.25 and X=3. Since we are working in the interval of (1,4), we can ignore 0.25
Thus our potential X values for max and min are X=1,X=4,X=3(You don't want to forget the ends of the bounds!)
Plugging these value in for f(x), we get
f(1)=2.833
f(3)=-8.5
f(4)=1.667
Thus X=1 is the max and X=3 is the min.
So max:(1,2.833)
min:(3,-8.5)
Hope this helps!
Short side length = x
Medium side = x + 7
Long side = 5x
Total 49, so
x + x + 7 + 5x = 49
If you combine like terms:
7x + 7 = 49
Subtract 7 from both sides
7x = 42
Divide both sides by 7
x = 6 inches.
