Question

Which number is not a perfect square a.5,329 b.1,280 c.3,600 d.729?

Answer 1

`1280` is not a square.

Explanation:

Of course you could use your calculator to find out, but in this case it can be done faster.

A square can never end in an odd number of zeroes. A zero at the end points to a factor `10or2*5`. In a square all factors are paired, so there should be an even number of zeroes.

BTW: this does not mean that every number ending in two zeroes is a square!

Answer 2

b. `1280` is not a perfect square.

Explanation:

a. `5329 = 73^2`
b. `1280 = 2^8*5 = (2^4)^2*5 = 16^2*5`
c. `3600 = 2^4*3^2*5^2 = (2^2*3*5)^2 = 60^2`
d. `729 = 3^6 = (3^3)^2 = 27^2`