chép mạng.

Hãy giải thích về gương cầu.

Goi x,y,z lan luot la so thu nhat nhat, thu 2 va thu 3 can tim. Theo de ta co:

2x = 3 y = 5z          => x lon nhat , z be nhat

Va: x-z = 72

=> \(\frac{x}{\frac{1}{2}}=\frac{y}{\frac{1}{3}}=\frac{z}{\frac{1}{5}}=\frac{x-z}{\frac{1}{2}-\frac{1}{5}}=\frac{72}{\frac{3}{10}}=240\)

=> y = 240 . 1/3 = 80

Vay: So thu 2 la 80

\(B=\sqrt{\left(3-x\right)^2+2\left(y+1\right)^2+3^2}+\sqrt{\left(x+2\right)^2+2^2}\ge\sqrt{\left(3-x+x+2\right)^2+\left(3+2\right)^2}=5\sqrt{2}\)

Bmin = \(5\sqrt{2}\) khi x=0 ; y =-1

B min nhé