3 times 6 18 and do that 6 times add
∈ ≤ ≥
-6 ≤ 2x + 6 ≤ 6 ( seperate the two inequalities)
2x + 6 ≥ - 6
2x + 6 ≤ 6 (solve the inequalities)
x ≥ -6
x ≤ 0 (find the intersection)
solution is : x ∈ { -6, 0 }
We will use double angle identities:
cos (5x ) = sin (10x )
cos (5x ) = 2 cos (5x ) sin ( 5x )
cos ( 5 x) - 2 cos ( 5 x ) sin ( 5x ) = 0
cos ( 5 x ) · [ 1 - 2 sin (5 x) ] = 0
cos ( 5 x ) = 0 or : 1 - 2 sin (5 x) = 0
5 x = π/2 +kπ, k∈Z sin (5 x) = 1/2
x1 = π/10 + kπ/5 5 x = π/6+2kπ , k∈ Z
5 x = 5π/6 +2kπ , k∈ Z
x 2 = π/30 +2kπ/5
x 3 = π/9 + 2kπ/5
The answer is b. Great job! here ill show you the work.
15x +90 > 270
move constant to the right side and change its sign, like this:
15x>270-90
then subtract the numbers
15x>180
lastly, divide both sides by 15.
hope this helped!
