Question

if p + 1/p =3 , the value of p - 1/p equals to what

Answer 1

p+1/p=3
from here..find value..of p..
p+1=3p
1=3p-p
1=2p
p=1/2

and it is 1/2
then put it in p-1/p..
1/2-1/1/2=-1
and the ans..is -1
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hope it helps u

Answer 2

Here squaring will work
 just remember that 
(a+b)² = (a-b)² - 4ab
we will use this later

now let's square both sides
$(p+\frac{1}{p}) ^{2} = 3^{2}$
$p^{2} + (\frac{1}{p}) ^{2}+ 2 =9$

now here we can write it as
${ (p+ \frac{1}{p} )^{2} + 2} + 2 = 9$
so
$(p- \frac{1}{p} )^{2} = 5$
$(p- \frac{1}{p} ) =\sqrt{5}$