As can be seen from the figure, the diameter of the bottom surface of the cylinder is x/2, which can be obtained by the length of the side surface of the cylinder = the circumference of the bottom surface.

π x/2= y-x/2, so y=π x/2+x/2=(π+ 1)/2 times x, so y is a proportional function of x, and of course x is greater than 0.

12 topic b

When x is less than 0, the program takes the reciprocal first, then multiplies it by 2, and finally takes the reciprocal. The result is that y=-2/x (1) is wrong.

Area of triangle POQ = area of triangle POM+area of triangle QOM. According to the function image, this is the image of two inverse proportional functions, so the area of triangle POM is a certain value K 1/2, and the area of triangle QOM is a certain value K2/2(K 1, K2 is assumed to be the proportional coefficient of two inverse proportional functions), so the area of triangle POM+the area of triangle QOM is a certain value, triangle.

When x is greater than 0, according to the program, the result is y= 4/x, which is an inverse proportional function. When k is greater than 0, the image is in one or three quadrants. The premise of this problem is that x is greater than 0, so the image is in the first quadrant, and y decreases (3) with the increase of x.

Therefore, according to (1)(3) wrong, choose B.