Ta co: a+b+c= a²+b²+c² =1

Va: x:y:z = a:b:c

CMR: (x+y+z)² = x²+y²+z²

                                               Giai

Ta co: x:y:z = a:b:c

=> x/a = y/b = z/c =  (x+y+z) / (a+b+c)

Suy ra: x/a = y/b = z/c  => x²/a² = y²/b² = z²/c² = (x²+c²+z²) / (a²+b²+c²)

Do a+b+c = a²+b²+c²  .Nen suy ra:

(x+y+z) = (x²+y²+z²)                   (dpcm)

N=\(\sqrt{3+2\sqrt{2}}\)+\(\sqrt{6-4\sqrt{2}}\)

=\(\sqrt{1+2\sqrt{2}+2}\)+\(\sqrt{4-2.2\sqrt{2}+2}\)

=\(\sqrt{\left(1+\sqrt{2}\right)^2}\)+\(\sqrt{\left(2-\sqrt{2}\right)^2}\)

=1+\(\sqrt{2}\)+2-\(\sqrt{2}\)=3

câu 1a

997²=997²-9+9

=(997-3)(997+3)+9

=1000.994+9=994000+9

=994009

10 giống đoàn tuấn khải

c, (n+6)²-(n-6)²=(n+6-n+6)(n+6+n-6)(hđt số 3

=12 .2n=24n