Question

I got this far in my working out and am already stuck. have i gone wrong?

Answer 1

Yes, you made an algebraic error. By multiplying 18 x 4, you messed up on order of operations.

(x+9)(x+2)*4

becomes:

(x^2+11x+18)*4

= 4x^2 + 44x + 72

anyway, this is how I would do this problem:

(x+9)(x+2)(4) = 912

(x+9)(x+2) = 228

x^2 + 11x + 18 = 228

x^2 + 11x - 220 = 0

(x+21)(x-10) = 0

x = -21 or 10

The dimensions can't be negative, so we only use x = 10

The dimensions are then 10+9, 10+2, 4

or 19, 12, 4