S=X(50-X)
S=400 X(50-X)=400 X²-50X+400=0 (X-10)(X-40)=0 X=10或40
S=625 X(50-X)=625 X²-50X+625=0 (x-25)²=0 X=25
S=X(50-X)=-(x-25)²+625≤625 S不可能等于700
S=X(50-X)
S=400 X(50-X)=400 X²-50X+400=0 (X-10)(X-40)=0 X=10或40
S=625 X(50-X)=625 X²-50X+625=0 (x-25)²=0 X=25
S=X(50-X)=-(x-25)²+625≤625 S不可能等于700