Cos(A-B) = cosAcosB + sinAsinB
<span>
cos(</span>π/2 - θ) = cos(π/2)cosθ + sin(π/2)sinθ
π/2 = 90°
cos(π/2) = cos90° = 0. sin(π/2) = sin90° = 1
cos(π/2 - θ) = cos(π/2)cosθ + sin(π/2)sin<span>θ
</span>
= 0*cosθ + 1*sin<span>θ = </span>sin<span>θ
Therefore </span>cos(π/2 - θ) = sin<span>θ
QED </span>
5y - 16 + 3y + 20 = 180 degrees
Combine like terms on the left side
8y + 4 = 180
Subtract 4 from both sides.
8y = 176
Divide both sides by 8
y = 22
Plug 22 into y for each angle.
3y + 20 = 3(22) + 20 = 66 + 20 = 86 degrees
5y - 16 = 5(22) - 16 = 110 - 16 = 94
The angle opposite 5y - 16 also equals 94 because they are vertical angles.
The angle opposite of 3y + 20 also equals 86 because they are vertical angles
Answer:
divide perimeter by 3
Step-by-step explanation:
all 3 sides of an equilateral triange are equal, so you can divide the perimeter by 3 to get the length of one side
