#965 · Algebra · Linear equations

Prove proportion identity

If $a, b, c, d$ are proportionals (i.e. $a : b = c : d$ ), prove that $a + d = b + c + \frac{( a - b ) ( a - c )}{a} .$

~8 minProof · checked by AIProportionalityAlgebraic manipulation

H. S. Hall & S. R. Knight, Higher Algebra (1891) · Ch. II. Proportion, Examples II, No. 16

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