If the product of the real roots of the above equation can be expressed as , where and , and , are coprime,
then find .
This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try
refreshing the page, (b) enabling javascript if it is disabled on your browser and,
finally, (c)
loading the
non-javascript version of this page
. We're sorry about the hassle.
We can multiply the first term with the fourth term, and the second one with the third one:
( 3 6 x 2 − 1 5 x + 1 ) ( 2 4 x 2 − 1 0 x + 1 ) = 5
( 3 ( 1 2 x 2 − 5 x ) + 1 ) ( 2 ( 1 2 x 2 − 5 x ) + 1 ) = 5
Now, let y = 1 2 x 2 − 5 x , so:
( 3 y + 1 ) ( 2 y + 1 ) = 5 6 y 2 + 5 y − 4 = 0 ( 3 y + 4 ) ( 2 y − 1 ) = 0 y 1 = − 3 4 y 2 = 2 1
From here we have two solutions for y , so there are two cases:
1 2 x 2 − 5 x = − 3 4 3 6 x 2 − 1 5 x + 4 = 0
The discriminant is Δ = ( − 1 5 ) 2 − 4 ( 3 6 ) ( 4 ) = − 3 5 1 < 0 , hence we don't have real roots.
The second case is:
1 2 x 2 − 5 x = 2 1 2 4 x 2 − 1 0 x − 1 = 0
The discriminant is Δ = ( − 1 0 ) 2 − 4 ( 2 4 ) ( − 1 ) = 1 9 6 > 0 , so there are two distinct real solutions, and their product, by Vieta's formulas is − 2 4 1 .
Comparing we get a = − 1 and b = 2 4 , thus the answer is ∣ a ∣ + b = 2 5 .