Step-by-step explanation:
2x-y=8
x+y=20
------------
3x=28
×=28÷3=9.3
so
9.3+y=20
y=20-9.3
y=20.7
Week 1: 50
2: 100
3: 200
4: 400
5: 800
6: 1600
7: 3200
8: 6400
Cos(θ) = -20/√((-20)^2 +(-21)^2)
.. = -20/-√841 . . . . . . . . . . . . . . . . . θ is a 4th-quadrant angle, so cos(θ) > 0
.. = 20/29
The value of the cosine is 20/29.
Answer: AC=12 cm
Step-by-step explanation:
To solve this problem you must apply the law of sines, as you can see below:

Where:
a=13
A=85.2°
B=71.6°
Therefore, you must solve for b, then, you obtain that the lenght AC asked in the problem above is:
