原式=900+3600x²=5625x² 900=2025x² x²=36/81
【∵36=±6x(±6) 81=±9x(±9)】∴ x=±(6/9)
原式=(X-50)[800-20(X-60)]=12000
(X-50)[800-20(X-50-10)]=12000
800X(x-50)-20(x-50)²+200(x-50)=12000
-20(x-50)²+1000(x-50)-12000=0
(x-50)²-50(x-50)+600=0
(x-50-30)(x-50-20)=0
x=80 或x=70
原式=X²=(X+1)²-(X-1)² X²=(X+1-X+1)(X+1+X-1) X²=4X X²-4X=0 X(X-4)=0
X=4或X=0
原式=π【(4/9)X(0.5X)²-(0.5x-3)²】=0 【∵4/9 = 2X2/(3X3)】
∴π【(2/3)²X(0.5X)²-(0.5x-3)²】=0
πX(2/3 -0.5x+3 )X(0.5X-0.5x+3)X(2/3 +0.5x-3 )X(0.5X+0.5x-3)=0
πX3X(11/3)X(0.5x-7/3)X(x-3)=0
11π(0.5x²-23/6x+7)=0
11π{0.5【x²-23/3x+(23/3)²】+7-529/18}=0
11π【0.5(x-23/3)²-403/18】=0
0.5(x-23/3)²-403/18=0
0.5(x-23/3)²=403/18
x=23/3±根号403/3=(23±根号403)/3
话说第四题我不能确定