Current location - Training Enrollment Network - Mathematics courses - 20 10 Tianjin senior high school entrance examination math problem 18 answer detailed explanation! Be specific! Especially the third question! ! ! ! ! !
20 10 Tianjin senior high school entrance examination math problem 18 answer detailed explanation! Be specific! Especially the third question! ! ! ! ! !
AD=C`D (the answer is not unique, but AE = c` f (Ⅱ) ① ② ③.

1. Because it is folded, DE=BE. Let AE=x, then BE=DE=(a-x). In Rt△ADE, AE is obtained by pythagorean theorem. +AD? =DE? What about x? +b? =(a-x)? , expand, a? -B? =2ax。

In a regular pentagon, ∠ c 'da = 108, ∠ ade = 108-90 = 18, while in Rt△ADE, AE = ad tan ∠ ade,

That is, x = b tan 18, then a? -B? =2a b tan 18