${(a+4)}^2=a^2+2\cdot a\cdot 4+4^2=a^2+8a+16\backslash left(a+4\backslash right)^2=a^2+2\backslash cdot\; a\backslash cdot4+4^2=a^2+8a+16$

${(4-a)}^2=4^2-2\cdot 4\cdot a+a^2=16-8a+a^2=a^2-8a+16\backslash left(4-a\backslash right)^2=4^2-2\backslash cdot4\backslash cdot\; a+a^2=16-8a+a^2=a^2-8a+16$

${(a-2)}^2=a^2-2\cdot a\cdot 2+2^2=a^2-4a+4\backslash left(a-2\backslash right)^2=a^2-2\backslash cdot\; a\backslash cdot2+2^2=a^2-4a+4$

${(a+2)}^2=a^2+2\cdot a\cdot 2+2^2=a^2+4a+4\backslash left(a+2\backslash right)^2=a^2+2\backslash cdot\; a\backslash cdot2+2^2=a^2+4a+4$

${(2-a)}^2=2^2-2\cdot a\cdot 2+a^2=4-4a+a^2=a^2-4a+4\backslash left(2-a\backslash right)^2=2^2-2\backslash cdot\; a\backslash cdot2+a^2=4-4a+a^2=a^2-4a+4$