[tex]a = ( {4}^{50} + {4}^{49} + {4}^{48} ) \div 21[/tex]
[tex]a = [ {4}^{48}( {4}^{2} + 4 + 1) ] \div 21[/tex]
[tex]a = [ {4}^{48}(16 + 4 + 1) ] \div 21[/tex]
[tex]a = ( {4}^{48} \times 21) \div 21[/tex]
[tex]a = {4}^{48} \times (21 \div 21)[/tex]
[tex]a = {4}^{48} \times 1[/tex]
[tex]a = {4}^{48} [/tex]
[tex]a = {4}^{24 \times 2} [/tex]
[tex]a = {( {4}^{24}) }^{2} = > p.p[/tex]
