Product proportion identity

If $a : b = c : d$ , and $e : f = g : h$ , prove that $a e + b f : a e - b f = c g + d h : c g - d h$ .

~10 minProof · checked by AIproportionscomponendo and dividendo

H. S. Hall & S. R. Knight, Higher Algebra (1891) · Ch. II. Proportion, Examples II, No. 12

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