Don't just write the factors down, write them multiplied to give 16, then add them: 16=16*1 when added give 16+1=17 16=8*2 when added give 8+2=10 16=4*4 when added give 4+4=8 So now you see that 4+4=8 is what you need, so you write: (x+4)(x+4) And since the factors are the same you write the answer in simplest form: (x+4)² Edwin