$解：?(1)\frac {sin 30°}{cos 30°}=\frac 12÷\frac {\sqrt 3}2=\frac {\sqrt 3}3=tan 30°?$
$對于任意銳角α，都有?\frac {sin α}{cosα}=tan α?$
$理由：如圖，?sin α=\frac ac，??cos α=\frac bc，??tan α=\frac ab?$
$∴?\frac {sin α}{cos α}=\frac ac÷\frac bc=\frac ab=tan α?$
$?(2)①cos^2 45°+sin^2 45°=(\frac {\sqrt 2}2)^2+(\frac {\sqrt 2}2)^2=\frac 12+\frac 12=1?$
$?②cos^2 60°+sin^2 60°=(\frac 12)^2+(\frac {\sqrt 3}2)^2=\frac 14+\frac 34=1?$
$發(fā)現(xiàn)：對于任意銳角α，都有?cos^2α+sin^2α=1?$
$理由：如圖，?sinα=\frac ac，??cosα=\frac bc?$
$?cos^2 α+sin^2 α=(\frac bc)^2+(\frac ac)^2=\frac {a^2+b^2}{c^2}=\frac {c^2}{c^2}=1?$
