Log21(3)*log21(21*7)+log²21(7)= log21(3)*( log21(21)+log21(7) )+log²21(7)= log21(3)*( 1+log21(7) )+log²21(7)=log21(3)+log21(3)* log21(7)+ log²21(7)= log21(3)+ log21(7)* ( log21(3)+ log21(7) ) = log21(3)+ log21(7)* log21(3*7)= log21(3)+ log21(7)=log21(3*7)=log21(21)=1