Răspuns :
a = 5 ; b = 2x+5 ; c = x²+9
r = b-a => r = 2x+5-5 = 2x
r = c-b => r = x²+9-2x-5 = x²-2x+4
x²-2x+4 = 2x => x²-4x+4 = 0 <=> (x-2)² = 0 => x-2 = 0 => x =2
a = 5 ; b = 9 ; c = 13 ; r = 4
a = 5 ; b = 2x+5 ; c = x²+9
r = b-a => r = 2x+5-5 = 2x
r = c-b => r = x²+9-2x-5 = x²-2x+4
x²-2x+4 = 2x => x²-4x+4 = 0 <=> (x-2)² = 0 => x-2 = 0 => x =2
a = 5 ; b = 9 ; c = 13 ; r = 4