S (ABCD) = AD * H =126
-2х+10+3х-12-4х-1=0
-3x=3
х=-1
1)925-825=100, 527+100=627
2) 2/19*19=2 ,2*13,5=27,27/4=6.75
3)2/17*17/21=2/21 , 3/11 * 4/3=4/11 , 2/21*4/11 = 8/231