As soon as I read this, the words "law of cosines" popped
into my head. I don't have a good intuitive feeling for the
law of cosines, but I went and looked it up (you probably
could have done that), and I found that it's exactly what
you need for this problem.
The "law of cosines" relates the lengths of the sides of any
triangle to the cosine of one of its angles ... just what we need,
since we know all the sides, and we want to find one of the angles.
To find angle-B, the law of cosines says
b² = a² + c² - 2 a c cosine(B)
B = angle-B
b = the side opposite angle-B = 1.4
a, c = the other 2 sides = 1 and 1.9
(1.4)² = (1)² + (1.9)² - (2 x 1 x 1.9) cos(B)
1.96 = (1) + (3.61) - (3.8) cos(B)
Add 3.8 cos(B) from each side:
1.96 + 3.8 cos(B) = 4.61
Subtract 1.96 from each side:
3.8 cos(B) = 2.65
Divide each side by 3.8 :
cos(B) = 0.69737 (rounded)
Whipping out the
trusty calculator:
B = the angle whose cosine is 0.69737
= 45.784° .
Now, for the first time, I'll take a deep breath, then hold it
while I look back at the question and see whether this is
anywhere near one of the choices ...
By gosh ! Choice 'B' is 45.8° ! yay !
I'll bet that's it !
Permafrost occurs in areas where the temperature of the ground remains below the freezing mark for two years or more. About a quarter of the Northern Hemisphere's landscape fits this definition. Most of the world's permafrost is found in northern Russia, Canada, Alaska, Iceland, and Scandinavia.
Answer:
x=y=z=90.
Step-by-step explanation:
let the 3 numbers be x,y,z.
let s be sum
s=x+y+z
we need to maximize xy+yz+zx
or , xy + y(270-(x+y))+x(270-(x+y)) = P(x)
Use Lagrange's Multipliers
⇒ΔP= λΔS
⇒
⇒y=x
⇒\frac{x+z}{x+y} =1
⇒z=y
⇒x=y=z
⇒3x = 270
⇒x= 90
hence, x=y=z=90.
