If a and B are real numbers and 1 / A-1 / b = 1 / (a + b), then the values of B / A-A / b are? A, - 1 B, 0 C, 1 / 2 D, 1 A、-1 B、0 C、1/2 D、1

If a and B are real numbers and 1 / A-1 / b = 1 / (a + b), then the values of B / A-A / b are? A, - 1 B, 0 C, 1 / 2 D, 1 A、-1 B、0 C、1/2 D、1

Multiply both sides of the known equation by a + B to get
(A+B)/A-(A+B)/B=1 ,
That is, (1 + B / a) - (A / B + 1) = 1,
B / A-A / b = 1
Choose D

If the three sides of △ ABC satisfy a2-2bc = c2-2ab, then △ ABC is ()
A. Isosceles triangle B. right triangle C. equilateral triangle D. acute triangle

The equation can be transformed as: a2-2bc-c2 + 2Ab = 0, (a2-c2) + (2ab-2bc) = 0, (a + C) (A-C) + 2B (A-C) = 0, (A-C) (a + C + 2b) = 0, ∵ a, B, C are the three sides of △ ABC, ∵ a + C + 2B > 0, ∵ a-c = 0, ∵ a = c.. The triangle is isosceles triangle, so a