S = 2 SAMD ABD3S + S = 2 (S + S )ADM BCN ABD BCD= 2 S
89.
S = 2 S
AMD
ABD
3
S + S = 2 (S + S )
ADM
BCN
ABD
BCD
= 2 S .
ABCD
S = S 1
BCM
BCA
ADN
ACD
S + S = S 1
ADN
BCM
ABCD
S + S + S + S = S
ADM
BCN
BCM
ADN
ABCD
Hay :S + S + S + S + (S
1
2
3
4
ADP
+ S
BQC
) × 2 = S
ABCD
Mặt khácS = S + S + S + S + (S + S ) + S .
ABCD
1
2
3
4
APD
BQC
MPNQ
VậyS
APD
+ S
BQC
= S
MNPQ