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)