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20 13 answers to Ningxia mathematics entrance examination
Solution:

As shown in the figure, if DE⊥AC is at point E, it is easy to get AE = ED = EA.

Let de = x, at Rt⊿DEC,

CE= 3 times CE = 3 under the root sign times x under the root sign.

When CB=25, CB=CE-BE.

∴x = 25+ x 3 times under the root sign.

∴x= 12.5 (3+ 1 under the root sign)

∴AB=2BE=2x=25 (3+1under the radical sign) = 25 (1.7+1) = 25 * 2.7 = 67.5 (in the sea).

So, it is right to keep dreaming.