Why can the calvin cycle work at night, but the photosystems cannot?

Because photosystems need light to operate (photo=light).

Photosystems use energy from sunlight, Calvin systems use energy stored in the plant.

Explanation:

The Calvin cycle is a dark reaction because it does not need sunlight. Although it can happen during the day, this process does not require energy from the sun to work. Other names for the Calvin cycle include the Calvin-Benson cycle, light-independent reaction, carbon fixation and C3 pathway.

complete the square on the right side of the equation;

-5(x + 0)^2 + 15

answer: d. y = -x^2 + 15

prism b but im not for sure