
3x+4y=123(rcosθ)+4(rsinθ)=12r(3cosθ+4sinθ)=12…(1)3(−rsinθ)+4(rcosθ)=12r(−3sinθ+4cosθ)=12…(2)(r12)2+(r12)2=(3cosθ+4sinθ)2+(−3sinθ+4cosθ)22(r12)2=9+16r22×144=25⇒288=25r2⇒25288=r2⇒2(512)=rℓ=OP2+PQ2+QO2ℓ=r2+r2+r2(cosθ+sinθ)2+r2(sinθ+cosθ)2=2r2+r2(1+sin2θ+1−2sin2θ)=2r2+2r2=4r2=4(25288)=251152=46.08[ℓ]=46