How do you solve the rational equation (x^2-7)/(x-4)=0?

2 Answers
Jan 11, 2016

x = ±sqrt7

Explanation:

for this rational function to equate to zero means that the numerator must be zero as the denominator ≠ 0

rArr x^2 - 7 = 0 rArr x^2 = 7 rArr x = ±sqrt7

Jan 11, 2016

x=+-sqrt(7)

Strong guidance given on manipulation!

Explanation:

Given: color(brown)(color(white)(....) (x^2-7)/(x-4)=0)

Multiply both sides by color(blue)((x-4))

color(brown)((x^2-7)/(x-4)color(blue)(xx(x-4))=0xxcolor(blue)((x-4))

(x^2-7) xx(x-4)/(x-4)=0

But (x-4)/(x-4)" is another way of writing " 1 giving:

(x^2-7) xx1=0
'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Add color(blue)(7) to both sides

color(brown)( x^2-7 color(blue)(+7) =0color(blue)(+7)

x^2=7
'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

so color(white)(...) x= sqrt(x^2) = +-sqrt(7)

'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The square root has to be +- because:

x^2=( + sqrt(7))xx (+sqrt(7) )-> "positive "x^2

And

x^2= (-sqrt(7))xx(-sqrt(7))-> "positive "x^2