This is valid through the law of syllogism. If you swap lines 1 and 2, then you'll have this argument:
If I step on a beehive, then I will get stung.
If I get stung by a bee, then it will hurt.
Therefore, if I step on a beehive, then it will hurt
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So it's like connecting a chain together. Point A (stepping on the hive), leads to point B (getting stung), which leads to point C (getting hurt). We can take a shortcut to bypass point B to jump from A to C in one step. Check out the attached image for a visual of what I'm referring to.
Answer:
•cos(s+t) = cos(s)cos(t) - sin(s)sin(t) = (-⅖).(-⅗) - (√21 /5).(⅘) = +6/25 - 4√21 /25 = (6-4√21)/25
•cos(s-t) = cos(s)cos(t) + sin(s)sin(t) = (-⅖).(-⅗) + (√21 /5).(⅘) = +6/25 + 4√21 /25 = (6+4√21)/25
cos(t) = ±√(1 - sin²(t)) → -√(1 - sin²(t)) = -√(1 - (⅘)²) = -⅗
sin(s) = ±√(1 - cos²(s)) → +√(1- cos²(s)) = +√(1 - (-⅖)²) = √21 /5
30 is the old value and 55 is the new value. In this case we have a positive change (increase) of 83.33333333 percent because the new value is greater than the old value. Using this tool you can find the percent increase for any value.
Answer: 
Step-by-step explanation:
Rewrite it in the form
, where 

Use Square of Sum: 
