2021-08-20

Dare2solve | Find max value of (a + c)(b + d)

This question was uploaded on my Instagram, Facebook and Twitter account on 19th of August 2021. You can check it on my Social media account. Kindly follow my accounts for daily new puzzles. You will get daily one puzzle at 4.00 UTC (Convert it as per your country timing).

Given that a² + b² = 16² , b² + c² = 24² , c² + d² = 42² and d² + a² = 38² then find max value of product of (a + c) and (b + d).

Give this question a try then check your answer with solution.

(Shortcut Image Solution with Calculations is gives below in this post)

This Algebraic question can be solved Geometrically,
It's diagram will be:
Here AC and DE are perpendicular to each other,
AB = a
BD = b
BC = c
BE = d
AD = 16
DC = 24
CE = 42
AE = 38

Note (a + c)(b + d) will give area of this figure since AC and DE are perpendicular to each other.

Here we can apply Ptolemy's Theorem to calculate product of diagonal.
(AC)(DE) = (AD)(CE) + (CD)(AE)
⇒ (a + c)(b + d) = (16)(42) + (24)(38) = 1584








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