Simplify 48 - 3 x squared over x squared +x-20

remember difference of 2 perfect squares,
a^2-b^2=(a+b)(a-b)
factor them to find ones

48-3x^2=3(16-x^2)=(3)(4+x)(4-x)

x^2+1x-20
find what 2 numbers multiply to -20 and add to 1
-4 and 5
(x-4)(x+5)

now we have

we can clear that (x-4) by force undistributing a negative 1 from that (4-x)
(4-x)=(-1)(x-4)
=
=
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