Question

b^2/16b^2-81:b/36b+81

Answer 1

b²/(16b²-81):b/(36b+81)=b²/(4b-9)(4b+9) *9(4b+9)/b=9b/(4b-9)
b=-9
9*(-9)/(-36-9)=-81/(-45)=9/5=1,8

Answer 2

$frac{ b^{2} }{(4b-9)(4b+9)} * frac{9* (4b+9)}{b} = frac{b}{4b-9} * frac{9}{1} = frac{9b}{4b-9} = frac{9* (-9)}{4*(-9)-9} = frac{-9*9}{-9*(4+1)} = frac{9}{5} =$ 1,8