This is my working:

x(2x-16)= 360

2x

^{2}-16x= 360

2x

^{2}-16x-360= 0

2(x

^{2}-8x-180)= 0

2(x-18)(x+10)= 0

x = 18 or -10

First pair: 18 and 10 (changing the ten from negative to positive)

I thought the second pair was just -18 and -10 but the textbook says -10 and -36. The quadratic formula of course just returns the same result as the factorisation above. I'm not sure how to arrive at the textbook's answer.