is the same thing here as the other triangles, the triangle below is an equilateral, the one above is an isosceles.
the <u>vertex</u> of the isosceles is 40°, so the twins angle at the <u>base</u> are (180 - 40)/2 = 70° = x each.
since the sides in the equilateral are all the same length, then 2y + 10 = x - y, but we already know what "x" is, so

That all dolphins have different sizes and are mostly different ages
It's going to be 2.4 * 10 to the power of 6.
Hope this helped =)
2018 is the 70th term of the progression.
Explanation
We start out finding the common difference of the progression:
46-17 = 29
Now we write the explicit formula for the sequence. It is of the form

We set this equal to 2018 to see if the answer is a whole number. If it is, it will be the term number that gives us 2018:
2018=17+29(n-1)
Using the distributive property,
2018=17+29*n-29*1
2018=17+29n-29
Combine like terms:
2018=29n-12
Add 12 to both sides:
2018+12=29n-12+12
2030=29n
Divide both sides by 29:
2030/29=29n/29
70=n
Since n=70, this means 2018 is the 70th term of the sequence.