1) a number multiplied by its reciprocal will always be 1, except for when the number is 0.
[tex]n * \frac{1}{n} = \frac{n}{n} = 1, n \neq 0[/tex]
So to verify if 2 numbers are reciprocals, just multiply them together and see if you get 1.
2) To estimate a sqrt, look at perfect squares.
10^2 = 100
11^2 = 121
12^2 = 144
13^2 = 169
14^2 = 196
15^2 = 225
16^2 = 256
221 is between 196 and 225, therefore sqrt(221) is between 14 and 15.
Much closer to 15
14.8^2 = 219
14.9^2 = 222
221 is closest to 222, so best estimate for sqrt(221) = 14.9
3)
Absolute value makes everything positive
|-3| = 3
