A8.0-cm-diameter disk emits light uniformly from its surface. 20 cm from this disk, along its axis, is an 8.0-cm-diameter opaque black disk; the faces of the two disks are parallel. 20 cm beyond the black disk is a white viewing screen. the lighted disk illuminates the screen, but there’s a shadow in the center due to the black disk. what is the diameter of the completely dark part of this shadow?

There is a lot more than this so I'm just gonna go into brief detail

Sixteen chemical elements are known to be important to a plant's growth and survival. The sixteen chemical elements are divided into two main groups: non-mineral and mineral.  

These nutrients are found in the air and water.  

In a process called photosynthesis, plants use energy from the sun to change carbon dioxide (CO2 - carbon and oxygen) and water (H2O- hydrogen and oxygen) into starches and sugars. These starches and sugars are the plant's food.  

Since plants get carbon, hydrogen, and oxygen from the air and water, there is little farmers and gardeners can do to control  how much of these nutrients a plant can use.

The 13 mineral nutrients, which come from the soil, are dissolved in water and absorbed through a plant's roots. There are not always enough of these nutrients in the soil for a plant to grow healthy. This is why many farmers and gardeners use fertilizers to add the nutrients to the soil.  

Macronutrients  

Macronutrients can be broken into two more groups:  

Primary and secondary nutrients.  

The primary nutrients are nitrogen (N), phosphorus (P), and potassium (K). These major nutrients usually are lacking from the soil first because plants use large amounts for their growth and survival.  

The secondary nutrients are calcium (Ca), magnesium (Mg), and sulfur (S). There are usually enough of these nutrients in the soil so fertilization is not always needed. Also, large amounts of Calcium and Magnesium are added when lime is applied to acidic soils. Sulfur is usually found in sufficient amounts from the slow decomposition of soil organic matter, an important reason for not throwing out grass clippings and leaves.  

Micronutrients  

Micronutrients are those elements essential for plant growth which are needed in only very small (micro) quantities . These elements are sometimes called minor elements or trace elements, but use of the term micronutrient is encouraged by the American Society of Agronomy and the Soil Science Society of America. The micronutrients are boron (B), copper (Cu), iron (Fe), chloride (Cl), manganese (Mn), molybdenum (Mo) and zinc (Zn). Recycling organic matter such as grass clippings and tree leaves is an excellent way of providing micronutrients (as well as macronutrients) to growing plants

Hope this helps

-IronWolfX