How do you solve #\frac { 12} { x } = \frac { 3x } { 100}#?

1 Answer
Gazza
Oct 15, 2017

#x=20 or x=-20#

Explanation:

#12/x = (3x)/100#
Cross multiply
#(12)(100)=(3x)(x)#
#1200 = 3x^2#
Now we need to subtract #color(red)(3x^2# from both sides
#1200 - color(red)(3x^2) = 3x^2 - color(red)(3x^2)#
#-3x^2 + 1200 = 0#
#-3x^2 = 0 -1200#
#-3x^2 = -1200#
Divide both sides by #color(purple)(-3)#
#(3x^2)/color(purple)(-3) = (-1200)/color(purple)(-3)#
#x^2 = 400#
Finally, take square root
#x= +-sqrt400#
#x = 20 or x=-20#

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