gwd math 30-9

aprilhuang

Q9:

Is the measure of one of the interior angles of quadrilateral ABCD equal to 60 degrees?

(1)   Two of the interior angles of ABCD are right angles.

(2) The degree measure of angle ABC is twice the degree measure of angle BCD.

这一题我觉得实e，但答案是c。我不明白的一点是怎麽分辨abc and bcd角是哪两个角呢？哪位可以帮我解释一下此题。谢了。

angelavivi

 from (1), it is inferred that the sum of the rest two angles is 360-90-90 = 180 degree.

from (2), angleABC = 2 angleBCD, so angle BCD has to be 180 degree, combined with condition (1).

windlake

a b c  and  b c d角是哪两个角呢？

B角和C角

aprilhuang

thanks  a  lot @