C-09-Q193mediumsingle_mcqIf 2cos(A+B)=12\cos(A + B) = 12cos(A+B)=1 and 2sin(A−B)=12\sin(A - B) = 12sin(A−B)=1 with A,BA, BA,B acute, then A=?A = ?A=?a30∘30^\circ30∘b45∘45^\circ45∘c60∘60^\circ60∘d15∘15^\circ15∘ব্যাখ্যাFrom cos(A+B)=12\cos(A+B)=\tfrac12cos(A+B)=21, A+B=60∘A+B=60^\circA+B=60∘, and from sin(A−B)=12\sin(A-B)=\tfrac12sin(A−B)=21, A−B=30∘A-B=30^\circA−B=30∘. Adding these gives 2A=90∘2A=90^\circ2A=90∘, so A=45∘A=45^\circA=45∘.