Решите пожалуйста 5-а² при а=1+√2

[latex]a=1+ \sqrt{2} \\ 5- a^{2} =5- (1+ \sqrt{2}) ^{2} = 5-(1^2+2*1* \sqrt{2}+ (\sqrt{2})^2 )= \\ =5- (1+ \sqrt{2}) ^{2} = 5-(1+2 \sqrt{2}+ 2 )=5- 1+ \sqrt{2} = \\ =5-1-2 \sqrt{2}- 2=2-2 \sqrt{2} [/latex]