1000cm^3 of metal is to be cast as a rectangular block with square ends. Use calculus to show that for the least surface area a rectangular the rectangular block needs to be a cube.
Having some trouble, just learned about optimization. Really would appreciate help!
My working was:
2x^2 + 4xl = SA
dSA/dx = 4x + 4l
4x + 4l = 0 (to find maximum)
4x = -4l
x = -l
I just carried on knowing I was on the wrong track, would love corrections. :)
(Some more working was l = (1000-2x^2)/4x but if I substitute that I need to deal with imaginary numbers, which isn't in this course but is in Mathematics: Specialist, that's how I know about it. :P )