The product of two integers of the same sign is always Positive.
Same sign (both positive or both negative) multiplication gives positive result.
Opposite signs give negative product.
The given proportion is x : 72 :: 7 : 18.
This can be rewritten as x/72 = 7/18.
To find x, cross-multiply:
x × 18 = 7 × 72
18x = 504
x = 504 / 18
x = 28
= √(200 + 6 × 10 - 4)/ 16
= √(200 + 60 - 4)/ 16
= √(260 - 4)/ 16
= √(256)/ 16
= 16 / 16
= 1