Answer:
As the property of tangent line of circle, the 2 right triangles ABC and ADC are congruent.
=> AB = AD or j = k
j = 25x^2 + 100x + 9
k = 21x^2 + 100x + 18
=> 25x^2 + 100x + 9 = 21x^2 + 100x + 18
=> 4x^2 = 9
=> x^2 = 9/4 = (3/2)^2
=> x = 3/2 ( -3/2 value is not valid)
Hope this helps!
:)
