11) Since the triangle has a pair of congruent base angles, it is an isosceles triangle which means that the two pairs of legs are congruent.
Make them equal to each other in an equation.
5x = x + 20
Subtract x from both sides.
4x = 20
Divide both sides by 4.
x = 5
12) The two legs are congruent so that means the base angles must be congruent. First find the measure of the base angles. Create an equation:
x + x + 50 = 180
Combine like terms.
2x + 50 = 180
Subtract 50 from both sides.
2x = 130
Divide both sides by 2.
x = 65
Now make the base angle plus x equal 180, because they form a straight line.
65 + x = 180
Subtract 65 from both sides.
x = 115
13) You know the vertex angle (top angle) is 90 degrees because it is supplementary to a right angle. The triangle is isosceles because the two legs are congruent, so make the base angles plus 90 add up to 180 in an equation.
x + x + 90 = 180
Combine like terms.
2x + 90 = 180
Subtract 90 from both sides.
2x = 90
Divide both sides by 2.
x = 45
For this case, we have by definition, that an irrational number is a number that can not be expressed as a fraction
, where a and b are integers and b is nonzero.
Some examples are:

So, that the answer is 
Answer:
Option C
We need to use the variables m and n to represent both numbers.
Their sum must equal -15. Therefore, we can write the next equation:
m + n = -15
If one number is five less than the other, we need to choose one variable and then we can write it in terms of the other variable. Then:
n = m-5
To find the value for each number, we can replace the n equation on the first equation:
m + n = -15
m + (m-5)= -15
Then:
m + m - 5 = -15
2m -5 = -15
Solve the equation for m:
Add both sides 5 units:
2m - 5 +5 = -15+5
2m = -10
Divide both sides by 2:
2m/2 = -10/2
m = -5
Finally, replace the m value on the first equation:
m + n = -15
-5 + n = -15
Then, solve the equation for n:
Add both sides by 5:
-5+5 + n = -15 +5
n = -10
Hence, both numbers are m=-5 and n= -10.
The equations separated by a comma are m + n = -15,n = m-5.
The numbers separated by a comma are -5,-10.
X + y = 180
x = 4y
Plug that in and you get: 4y + y = 180
5y = 180
y = 36
If you want the larger angle, simply plug in y to x = 4y
So: x = 4(36) = 144
The smaller angle is 36 degrees, and the larger angle is 144 degrees.