25a-5b-8 25a-5b-8:5a4b

25·a^(-5)·b^(-8) : 5·a^4·b

=   [ 25·a^(-5)·b^(-8) ] / [ 5·a^4·b ]             (ratios indicate division)

=   [ 25 / ( a^5 · b^8 ) ] / [ 5·a^4·b ]     (negative exponents become positive when placed in the denominator)

=   [ 25 / ( a^5 · b^8 ) ]  ·  [ 1 / ( 5·a^4·b ) ]    (division is replaced by multiplication of the reciprocal)

=   [ 25 · 1 ] / [ a^5 · b^8 · 5·a^4·b ]     (multiplying numerators times nums and denominators time denoms)

=   25 / [ 5 · a^9 ·  b^9 ]                                 (simplifying)

=   5 / [ a^9 · b^9 ]                                        (cancelling like factors)