Move words to the blanks and equations to the boxes to prove that vertical angles <21 and <23 are congruent.

See proof below

Step-by-step explanation:

From the given diagram, we can see that <2 and <3 lies on the same straight line, hence the sum of the angles is 180 degrees (supplementary)

<2 + <3 = 180 1

Similarly. <1 and <2 are also supplementary angles

<1 + <2 = 180 2

Subtract 1 from 2;

<3 - < 1 + <2 - <2 = 180 - 180

<3 - <1 +0 = 0

<3 - <1 = 0

Add <1 to both sides

<3 - <1 + <1 = 0+<1

<3 = <1 (Proved!)

This shows that <3 and <1 are equal

We can also conclude that <3 and <1 are vertically opposite angles and vertically opposite angles are equal

introduction, methodology, results, discussion

step-by-step explanation:

an observational study is one which consists of actual observation to record data and then analyse the data.

there are a number of factors that should be analyzed before starting an observational study.

the main four factors are:

i) introduction:   this should be analysed to check whether the purpose of the study is correctly established and the data recorded are appropriate for the study

methodology:   the method of collecting the data, such as whether randomly selected, and whether sample size matches with the population to be studied, whether questions asked are easy to answer by common men, etc.

results: then results such as summary of data with comments should be studied thoroughly

discussion:   the last is the discussion, this can be either by management people or persons who are all interested , etc.