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
90 × 7 = 630 , it's not hard, it's easy
Answer:
<u>Given </u>
A
<u>Find the inverse of f(x):</u>
- x = 3 + 6f⁻¹(x)
- 6f⁻¹(x) = x - 3
- f⁻¹(x) = (x - 3) / 6
B
- f · f⁻¹( ∛5/6) =
- f( f⁻¹( ∛5/6)) =
- f((∛5/6 - 3)/6) =
- 3 + 6((∛5/6 - 3)/6) =
- 3 + ∛5/6 - 3 =
- ∛5/6
C
- f · f⁻¹(x) =
- f(f⁻¹(x)) =
- f((x - 3)/6) =
- 3 + 6(x - 3)/6 =
- 3 + x - 3 =
- x
8513 is NOT divisible by 9, because the some of its digits (8+5+1+3) = 17 which is not divisible by 9 (answer B)
The answer is the third option which is AEF and FED, AEG and CEG
