解：設(shè)昆蟲(chóng)鳴叫次數(shù)?$ x $?與氣溫?$ y $?的關(guān)系為?$y= kx + b $?
將?$x=40，$??$y=30$?和?$ x=80 ，$??$ y=40 $?代入
得?$\begin {cases}30=40x+b\\40 = 80k + b\end {cases}，$?解得?$\begin {cases}{k=\frac 14 }\\{ b=20 }\end {cases}$?
∴?$y=\frac 14x+20$?
當(dāng)?$ x=56 $?時(shí)，?$ y=\frac 14×56+20=34$?
