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How do you solve $\frac{4}{b - 3.9} = \frac{2}{b + 1}$ $4/(b-3.9)=2/(b+1)$ ?

1 Answer

Jul 29, 2017

$b = - 5.9$ $color(green)(b=-5.9)$

Explanation:

Given
$xxx \frac{4}{b - 3.9} = \frac{2}{b + 1}$ $color(white)("xxx")4/(b-3.9)=2/(b+1)$

If we multiply both sides by $(b - 3.9) (b + 1)$ $(b-3.9)(b+1)$
(sometimes called "cross-multiplying")
we get
$xxx 4 (b + 1) = 2 (b - 3.9)$ $color(white)("xxx")4(b+1)=2(b-3.9)$

Expanding
$xxx 4 b + 4 = 2 b - 7.8$ $color(white)("xxx")4b+4=2b-7.8$

Simplifying
$xxx 2 b = - 11.8$ $color(white)("xxx")2b=-11.8$

$xxx b = - 5.9$ $color(white)("xxx")b=-5.9$

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