1 2 3 4 5 =200 Adding addition, subtraction, multiplication and division to the left side of the equation can sum two numbers into one number, or add brackets, but the order cannot be changed to make the equation hold Example (1 + 23) * 4-5 = 91, but it is not equal to 200

1 2 3 4 5 =200 Adding addition, subtraction, multiplication and division to the left side of the equation can sum two numbers into one number, or add brackets, but the order cannot be changed to make the equation hold Example (1 + 23) * 4-5 = 91, but it is not equal to 200

（1+3+4）*5^2=8*25=200
（12×3+4）×5=200

Calculation: (1 × 2 × 3 × ×11）÷（1+2+3+… +11）=______ ．

（1×2×3×… ×11）÷（1+2+3+… +11）=（1×2×3×… ×11）÷[（1+11）×11÷2]，=（1×2×3×… ×11）÷66，=（1×2×3×… ×11）÷（2×3×11），=1×4×5×6×7×8×9×10，=604800．

Known inequality system > = 0, Y > = 0, y

Choose D
Draw two straight lines and X, Y axis, four lines in the first quadrant of the quadrangle is the theme figure
Divide it into a right trapezoid and a right triangle
The intersection is (1,2)

The focus of the ellipse x ^ 2 / 9 + y ^ 2 / 4 = 1 is F1 and F2. The point P is the moving point on the ellipse. When the vector Pf1 * PF2 is less than 0, the value range of abscissa of point P is determined

Let the abscissa of point p be X
PF1=ex+a PF2=ex-a
There should be Pf1 ^ 2 + PF2 ^ 2 < F1F2 ^ 2
That is, (ex + a) ^ 2 + (ex-a) ^ 2 < 4C ^ 2
e^2*x^2＜2c^2-a^2
x^2＜9/5
-3 pieces 5 / 5 ＜ x ＜ 3 pieces 5 / 5