1.

Let a, b be integers such that all the roots of the equation (x2 + ax + 20)(a2 + 17x + b) = 0 are negative integers. What is the smallest possible value of a + b?

Answer»

∵ Roots of (x2 + ax + 20)(a2 + 17x + b) = 0 are negative integers and we required (a + b)min 

∴ a, b each should be minimum

a2 – 80 is perfect square and a is a positive integer

⇒ amin = 9

289 – 4b is a perfect square and b is a positive integer

⇒ bmin = 16                   (using 8, 15, 17)

∴ (a + b)min = 25



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