find a and b
Multiply the L term of the equation by ( 4+sqrt15) / (4+sqrt15)
to get (4+sqrt15)^2 / (1)
Mutiply the next term be (4-sqrt15)/ (4-sqrt15) to get
(4-sqrt15)^2 / (1)
then you have
16 +8 sqrt 15 + 15 + 16 - 8sqrt15 +15 = 62 + 0 sqrt15