cos (2x) = cos x
2 cos^2 x -1 = cos x using the double angle formula
2 cos ^2 x -cos x -1 =0
factor
(2 cos x+1) ( cos x -1) = 0
using the zero product property
2 cos x+1 =0 cos x -1 =0
2 cos x = -1 cos x =1
cos x = -1/2 cos x=1
taking the arccos of each side
arccos cos x = arccos (-1/2) arccos cos x = arccos 1
x = 120 degrees x=-120 degrees x=0
remember you get 2 values ( 2nd and 3rd quadrant)
these are the principal values
now we need to add 360
x = 120+ 360n x=-120+ 360n x = 0 + 360n where n is an integer
3 feet from each end of the mantel
Answer:
answer in photo
hope this helps :)
Step-by-step explanation:
<span>4(x+5) = 4x +5x
Simplify by distributing and combining like terms
</span>(4)(x)+(4)(5)=4x+5x
4x+20=4x+5x
4x+20=(4x+5x)
4x+20=9x
Subtract 9x from each side
4x+20−9x=9x−9x
5x+20=0
<span />
Subtract 20 from each side
−5x+20−20=0−20
−5x=−20
Divide each side by -5
-5x ÷ -5 = -20 ÷ -5
x = 4
P.S this was actually harder than most algebra problems, so don't beat yourself about it :D<span /><span /><span /><span /><span />
