How do you substitute 7x+2y=-19 and -x+2y=21

2 answers:

8 0

Steps:
1. Take -x + 2y= 21
2. Add x on both sides
2y= x + 21
3. Divide everything by 2
Y= 1/2x + 10.5
4. Substitute the y in 7x + 2y= -19 for 1/2x + 10.5
7x + 2(1/2x + 10.5)= -19
5. Multiply everything in parentheses
7x + x + 21= -19
8x + 21= -19
6. Subtract 21 on both sides
7. 8x=-40
8. Divide each side be 8
9. Your answer is
X=-5

mina [271]3 years ago

6 0

It's easier to use -x +2y = 21
so make it all = to x
should come out to x= 2y - 21
now substitute what you just found = to x into the other equation
7 (2y - 21) + 2y = - 19
now distribute and simplify
14y - 147 + 2y = -19
16 y = 128
y = 8

now substitute 8 for y in either equation
-x + 2( 8) = 21
-x = 5
x = -5

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A kite flying in the air has an 7-ft line attached to it. Its line is pulled taut and casts a 5-ft shadow find the heights of th

Stels [109]

The height of the kite is 4.89 feet

Explanation

The length of the line attached to the kite=7 feet

The length of the shadow that is cast on the ground=5 feet

the system forms a right angled triangle where the taught string of the kite is the hypotenuse, the shadow is the base and the height of the kite above the ground is the height.

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$h^2+b^2=H^2\\h^2=H^2-b^2\\h^2=7^2-5^2\\=49-25\\=24\\h=\sqrt{24\\} =2\sqrt{6} \\=4.89 feet$