Answer:
B.0.25
Step-by-step explanation:
Answer:
Step-by-step explanation:
P=5/25=1/5=0.20
Solve cos(4x)-cos(2x)=0 ∀ 0<=x<=2pi ..............(0)
Normal solution:
1. use the double angle formula to decompose, and recall cos^2(x)+sin^2(x)=1
cos(4x)=cos^2(2x)-sin^2(2x)=2cos^2(2x)-1 .................(1)
2. substitute (1) in (0)
2cos^2(2x)-1-cos(2x)=0
3. substitute u=cos(2x)
2u^2-u-1=0
4. Solve for x
factor
(u-1)(u+1/2)=0
=> u=1 or u=-1/2
However, since cos(x) is an even function, so solutions to
{cos(2x)=1, cos(-2x)=1, cos(2x)=-1/2 and cos(-2x)} ...........(2)
are all solutions.
5. The cosine function is symmetrical about pi, therefore
cos(-2x)=cos(2*pi-2x),
solution (2) above becomes
{cos(2x)=1, cos(2pi-2x)=1, cos(2x)=-1/2, cos(2pi-2x)=-1/2}
6. Solve each case
cos(2x)=1 => x=0
cos(2pi-2x)=1 => cos(2pi-0)=1 => x=pi
cos(2x)=-1/2 => 2x=2pi/3 or 2x=4pi/3 => x=pi/3 or 2pi/3
cos(2pi-2x)=-1/2 => 2pi-2x=2pi/3 or 2pi-2x=4pi/3 => x=2pi/3 or x=4pi/3
Summing up,
x={0,pi/3, 2pi/3, pi, 4pi/3}
<em>FIRST QUESTION:</em>
The slide is 21 ft long. You can imagine that this slide is actually the <u>hypotenuse</u> of a right angled triangle.
To get to the top of the slide you must climb up a vertical 9 foot ladder. You can imagine that this ladder is the <u>opposite</u> side of the right angled triangle.
Now, the distance between the bottom of the ladder and the bottom of the slide can be thought of as the <u>adjacent</u> side of this right angled triangle.
We know, thanks to Pythagoras that:
A²+O²=H²
A = Adjacent length = b
O = Opposite length
H = Hypotenuse
Therefore:
b²+9²=21²
b²=21²-9²
b²=360
b=√360=18.97 (2dp)
So the answer you are looking for is <u>19 feet</u> to the nearest tenth (answer: B).
<em>SECOND QUESTION:</em>
18²+24²=30² (Yes)
Therefore the answer to the second question is YES (answer: A).
