# More fun in 2015, Part 15

Algebra Level 2

$\large \begin{cases} {a_n=a_{n-1}a_{n-2}-b_{n-1}b_{n-2} } \\ { b_n=b_{n-1}a_{n-2}+a_{n-1}b_{n-2} } \end{cases}$

Two sequences $$a_n$$ and $$b_n$$ begin with values $$a_1=b_1=a_2=b_2=1$$ and satisfy the recursive relations above for $$n>2$$.

Find $$\large \frac{b_{2015}}{a_{2015}}$$.

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