$解：?(1)①tan A=\frac {BC}{AC}=\frac 34，??tan B=\frac {AC}{BC}=\frac 43?$
$②在?Rt△ABC?中，∵?AB=13，??AC=5?$
$∴?BC=\sqrt {AB^2-AC^2}=12?$
$∴?tan A=\frac {BC}{AC}=\frac {12}{5}，??tan B=\frac {AC}{BC}=\frac {5}{12}?$
$③在?Rt△ABC?中，∵?AB=25，??AC=24?$
$∴?BC=\sqrt {AB^2-AC^2}=7?$
$∴?tan A=\frac {BC}{AC}=\frac {7}{24}，??tan B=\frac {AC}{BC}=\frac {24}{7}?$
$?(2)?當(dāng)?∠A+∠B=90°?是，?tan A · tan B=1，?即互余兩角的正切互為倒數(shù)$
