Answer:
20
Step-by-step explanation:
y^2+4y-1=(-7)^2+4(-7)-1=(-7)(-7)-28-1=49-28-1=21-1=20
The row echelon form of the matrix is presented as follows;

<h3>What is the row echelon form of a matrix?</h3>
The row echelon form of a matrix has the rows consisting entirely of zeros at the bottom, and the first entry of a row that is not entirely zero is a one.
The given matrix is presented as follows;

The conditions of a matrix in the row echelon form are as follows;
- There are row having nonzero entries above the zero rows.
- The first nonzero entry in a nonzero row is a one.
- The location of the leading one in a nonzero row is to the left of the leading one in the next lower rows.
Dividing Row 1 by -3 gives:

Multiplying Row 1 by 2 and subtracting the result from Row 2 gives;

Subtracting Row 1 from Row 3 gives;

Adding Row 2 to Row 3 gives;

Dividing Row 2 by -2, and Row 3 by 18 gives;

The above matrix is in the row echelon form
Learn more about the row echelon form here:
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Answer:
16 years
Step-by-step explanation:
Given data
For the first tree
let the expression for the height be
y=4+x--------------1
where y= the total height
4= the initial height
x= the number of years
For the second tree, the expression is
y=12+0.5x-------------2
Equate 1 and 2
4+x=12+0.5x
x-0.5x=12-4
0.5x= 8
x= 8/0.5
x=16
Hence it will take 16 years for both trees to have the same height
The solution would be: a = 3/4
6[13-2(4+1)]
Solve what is in the bracket first.
Parenthesis first.
6[13-8-2]
6(3)
18