Algebra

Find all values of c such that c/(c - 5) = 4/(c + 4).

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\(\frac{c}{c-5}=\frac{4}{c+4}\\ c^2+4c=4c-20\\ c^2=-1\cdot 2^2\cdot 5\)

\(c=2i \sqrt{5}\)

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Find all values of c such that c/(c - 5) = 4/(c + 4).  

Cross multiply                     c • (c + 4)  =  4 • (c – 5)  

Multiply it out                           c² + 4c  =  4c – 20  

Subtract 4c from both sides            c²  =  –20

Square root of both sides                  c  =  +sqrt(–20)