We're going to solve each of the systems to determine the solution.
<u>System
</u>

using a graph tool
the solution is the line 
see the attached figure N 
<u>System
</u>

using a graph tool
the solution is the shaded area
see the attached figure N 
<u>System
</u>

using a graph tool
The system has no solution
see the attached figure N 
<u>System
</u>

using a graph tool
the solution is the shaded area
see the attached figure N 
therefore
<u>the answer is</u>
<u>System
</u>

Answer:
t=2.08 seconds.
Step-by-step explanation:
Well, in this example, H(t)=-0.6cos(2pi/2.5)t+1.5 should be equal to 1.2. If calculated, -0.6cos(0.8pi)t=1.2-1.5 which is equal to -0.6cos(0.8pi)t=-0.3, then cos(0.8pi)t=0.5. The value of cosine in terms of radians when it is equal to 0.5 is pi/3. So, cos(0.8pi)t=cos(pi/3). If simplified, (0.8pi)*t=5pi/3. pi's are cancelled out and t is calculated as 2.08333... If rounded to the nearest hundredth it is 2.08.
Answer:$9
Step-by-step explanation:
Let the additional amount be c
Total amount to spend on gift is $27
He had spent $18 so far
$18+c= $27
C= $27-$18
C=$9