# Another quad formula word prob

• Aug 28th 2009, 05:30 AM
RaphaelB30
Block 4 by 5 by 3 feet. Wants to reduce volume by shaving off the same amount from length width and height.

Could you give me a clue as to where I should start? I know I have to make a quad formula.

• Aug 28th 2009, 05:44 AM
RobLikesBrunch
$V=h \cdot l \cdot w$

If we're subtracting the same amount from each value:

$V=(h-x)(l-x)(w-x)$

Substitute in for the values of h, w, and l:

$V=(4-x)(5-x)(3-x)$

Multiply it out:

$V= (20-9x+x^2)(3-x)$

$V= 60-27x+3x^2-20x+9x^2-x^3 = -x^3+12x^2-47x+60$

Also, it isn't quadratic, but rather, a cubic...but I suppose you make a quadratic in one of the intermediate steps.