So Mn∨DC.

Because of MN? Flat ADC, DC? Planar ADC',

So MN∑ planar ADC'.

Similarly, ng sigma planar ADC.

And because MN∩NG=N,

So the plane GNM∑ sigma plane ADC'.

② Because ∠ bad = 90, so AD ⊥ ab.

Because AD⊥C'B and AB∩C'B=B,

So AD⊥ plane c' ab.

Because of C'A? The plane is C'AB, so the advertisement is ⊥ c 'a.

Because △BCD is an equilateral triangle, AB=AD,

If AB= 1 is not set, then? You can get BC=CD=BD=2, c' a = 1.

AB ⊥ C 'a can be obtained from the inverse theorem of Pythagorean theorem.

Because AB∩AD=A, C'A⊥ plane Abd ... (14 points)