( √15 + √3) / ( √15 - √3) = a + b √15
Rationlize it
(√15 +√3) / (√15 - √3) * (√15 + √3) / (√15 + √3) = (18 + 2√45 ) /1 2 = 3+ (1/3)√45
a+b√45=2/3+1/6√45
a=2/3
b√45=(1/6)√45
b=1/6
Answer: a = 2/3 , b = 1/6
i think there is a mistake occured in the question.wish this will be the right one you wants
hope it helps