Since this is an arithmetic sequence, you can conclude that
the addition to the number is constant.
Let x = the number asked
k = constant
number added to the sequence
7 + k = x
x + k = 17
Solve the system of equation:
7 + k + k = 17
7 + 2k = 17
2k = 10
k = 5
Therefore, the missing number is 12 (7 + 5).
Answer:
5
Step-by-step explanation:

=
=
=5
I think that you are mistaking the memory tool for something else
or a math book is trying to make math cute by calling them 'socatoa joe' and 'mr. pi' and such
anyway, SOH, CAH, TOA is the way to remember
Sine=oposite/hypotonuse
Cosine=adjacent/hypotonuse
Tangent=oposite/adjacent
(oposite side=side oposite the angle
adjacent is the side touching the angle that is not they hypotonuse
and of course the hypotonuse is the longest side aka, side oposite right angle)