Let∠idenoteincidenceangleand∠rdenoterefractedangle.Given:∠i=2×∠rNowbysnell′sLawapplingatinterfaceofism:sinisinr=sin(2r)sinr=2sinr×cosrsinr=2cosr=√2wherewehaveusedtrignometricidentity;sin2r=2sinx×cosxThereforewehave;cosr=√22=1√2⇒r=450nowwehave3relationfromaminimumdeviation;A=r1+r2A=2rA=900