Watch the scarecrow at the end of the Wizard of Oz when he receives a diploma and declares “the sum of the square roots of any two sides of an isosceles triangle is equal to the square root of the other side.”
For 80 years audiences believed him because he said it with confidence.
But, he was wrong! The sum of the square roots of two sides of a right triangle is equal to the square root of the hypotenuse.
Speak confidently, my friend, and know your geometry.