Why does $2x_1x_2y_1y_2 \leq x_1^2y_2^2+x_2^2y_1^2$?

75 Views Asked by At

When I tried to prove the triangle inequality $|z_1+z_2| \leq |z_1| + |z_2|$ algebraically for complex variables $z_1$ and $z_2$, I came across this inequality and found that this is always true no matter what. Can anyone explain why?

1

There are 1 best solutions below

0
On BEST ANSWER

Hint

Develop $(x_1y_2-x_2y_1)^2\ge0$.