The mathematical word describing both
and
in the expression
is "<u><em>addition</em></u>"
<h3>How to form mathematical expression from the given description?</h3>
You can represent the unknown amounts by the use of variables. Follow whatever the description is and convert it one by one mathematically. For example if it is asked to increase some item by 4 , then you can add 4 in that item to increase it by 4. If something is for example, doubled, then you can multiply that thing by 2 and so on methods can be used to convert description to mathematical expressions.
For the given case, the terms were
and
and the expression formed from them is 
This means both the terms were added together, as denoted by '+' (called 'plus') sign.
When two terms are written with 'plus' sign in between, then that means they're added to each other and the result will be addition of both of their's values.
Thus, the mathematical word describing both
and
in the expression
is <u><em>addition</em></u>"
Learn more about addition here:
brainly.com/question/14148883
Answer : The substances half life in days is, 5.6 days.
Step-by-step explanation :
Half life : It is defined as the amount of time taken by a radioactive material to decay to half of its original value.
All radioactive decays follow first order kinetics.
The relation between the half-life and rate constant is:

where,
k = rate constant = 0.1235 per days
= half-life
Now put all the given values in the above formula, we get:


Thus, the substances half life in days is, 5.6 days.
A principle square root of a real number that's not negative, such as 49,
is the square root of that number that is not negative.If you take the square root of 49, you get either -7 or 7, since both

and

equal 49. However, the principle square root would be
A) 7, since it's not negative.