We know that
applying the law of cosines
a² = b²+ c²<span> – 2*b*c*cos(A)
</span>
in this problem
a=?
b=20
c=9
A=90°
so
a² = b²+ c² – 2*b*c*cos(A)
but
cos (A)=0
a² = b²+ c²-----> 20²+9²----> a²=400+81----> a²=481-----> a=√481
a=21.93-----> a=22
the answer is
22
Hello again Charlesbabegirl! :)
First of all, let's say that the sum of all internal angles of a triangle is always 180°
This means that if you add up angles A, B and C you get 180 but we should find first the value of x by setting up a proportion of this type:
A + B + C = 180
12x + 12 + 15 + 3x + 18 = 180
Move all the known terms (those that don't have x) to the right with changed sign.
12x + 3x = 180 - 12 - 15 - 18
15x = 135
Divide both terms by 15
x = 9
Then plug the value of x...
m∠A = 12(9) + 12 = 108+12 = 120°
m∠C = 3(9) + 18 = 27 + 18 = 45°
Hope I helped and let me know if I was right!
The answer is approximately 11.18.