s^2 + s^2 = d^2 where d is the diagonal and s is the side.
<u><em>Givens</em></u>
P = 24
<u><em>Solution</em></u>
P = 4s Substitute for s
24 = 4*s Divide by 4
24/4 = s
s = 6
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d^2 = s^2 + s^2
d^2 = 6^2 + 6^2
d^2 = 36 + 26
d^2 = 72
d = sqrt(72)
Factors of 72
72: 6 * 6 * 2
<em><u>Rule</u></em>: Every pair of = factors allows you to take one of them outside the sqrt sign and throw the other a way. If there are no pairs, whatever you started with stays under the root sign.
Multiples of 15 are: 15,30,45,60,75,90,105,120,135,150,165,180,195,210,225,240,255,270,285,300,315,330,345,360,375,390,405,420,435,450,465,480,495,510,525,540,555,570,585,600,615,630,645,660,675,690,705,720,735,