Actually, this is not about angles. It's about the length of the sides in a right triangle.
In EVERY right triangle, the squares of the lengths of the short sides add up
to the square of the length of the longest side. You're in high school math,so
I'm SURE you've heard that in class before ... possibly even just before you
were assigned this problem.
Let's say that again: The squares of the lengths of the sides that meet at
the right angle add up to the square of the length of the longest side. In
the triangle in this particular problem, that means
a² + b² = c²
You know the lengths of 'b' and 'c', so you shouldn't have any trouble finding
the length of 'a'.
Answer:

Step-by-step explanation:
Given,
Art electives = 3,
History electives = 4,
Computer electives = 5,
Total number of electives = 3 + 4 + 5 = 12,
Since, if a student chooses an art elective and a history elective,
So, the total combination of choosing an art elective and a history elective = 
Also, the total combination of choosing any 2 subjects out of 12 subjects = 
Hence, the probability that a student chooses an art elective and a history elective = 

Which is the required expression.
Answer:
5x280=1400
Step-by-step explanation:
$1400
if he works on the weekends then add 580
s0 $1980
20/t=v and 12/t=(v-4) solve both for t
t=20/v and t=12/(v-4) since t=t
20/v=12/(v-4) cross multiplying...
20v-80=12v
8v-80=0
8v=80
v=10mph
The outbound speed was 10mph