Factor completely: x2-4

(x+2)(x-2)

Step-by-step explanation

x times x equals x^2, 2 times x equals 2x, -2 times x equals -2x, and 2 times -2 equals -4. If you add that up, the x-values cancel out, leaving the x^2 and the -4. (This explanation is working it backwards which is the easiest way IMO)

i think it would be 42cm