(a+b) + c = a + (b + c)
re-arrange the numbers - associative property of addition
Answer
Associative property of addition
Answer: (1,-1)
Step-by-step explanation:
- You can multiply the first equation by -1
- Add the equations.
- Solve for x, as following:

- Substitute the value of x into any of the original equations and then you must solve for y:

Therefore, the solution is: (1,-1)
Solution:
Let x represent a number of calling minutes. According to the problem, we want:

now, putting the similar terms together, we obtain:

this is equivalent to:

now, solving for x, we get:

then, the correct answer for the first question is:
400 minutes is the number of minutes the two plans cost the same
now, for the second question, we can replace the above value (400 minutes) into the following equation:

so that, the correct answer for the second question is:
$55 is the cost when the two plans cost the same
Answer:
25(a-2)(a+2)
Step-by-step explanation:
25a^2 -100
We can factor out 25
25(a^2 -4)
a^2 -4 is the difference of squares a^2-b^2= (a-b)(a+b)
where a =a and b=2
a^2 -4 = (a-2)(a+2)
25a^2 -100 = 25(a-2)(a+2)