Find the coordinates of the vertices formed by the system of inequalities.
x + y ≤ 9
y ­- 2x ≥ -21
y ≥ -4x + 15
a (­6, ­-9), (10, ­-1), (2, 7)
b (­-9,- ­6), (-­1, 10), (7, 2)
c (­-30, ­-21), (­-6, -9), (6, 15)
d (­-6, ­-9), (6, ­-3), (-­12, ­-21)

A

Step-by-step explanation:

To find the coordinates of the vertices , treat the inequalities as equations and solve them in pairs, simultaneously, that is

x + y = 9 → (1)

y - 2x = - 21 → (2) ← add 2x to both sides

y = - 21 + 2x → (3)

Substitute y = - 21 + 2x into (1)

x - 21 + 2x = 9

3x - 21 = 9 ( add 21 to both sides )

3x = 30 ( divide both sides by 3 )

x = 10

Substitute x = 10 into (3)

y = - 21 + 20 = - 1

Coordinates of vertex = (10, - 1 )

y - 2x = - 21 → (1)

y = - 4x + 15 → (2)

Substitute y = - 4x + 15 into (1)

- 4x + 15 - 2x = - 21

- 6x + 15 = - 21 ( subtract 15 from both sides )

- 6x = - 36 ( divide both sides by - 6 )

x = 6

Substitute x = 6 into (2)

y = - 24 + 15 = - 9

Coordinates of vertex = (6, - 9 )

x + y = 9 → (1)

y = - 4x + 15 → (2)

Substitute y = - 4x + 15 into (1)

x - 4x + 15 = 9

- 3x + 15 = 9 ( subtract 15 from both sides )

- 3x = - 6 ( divide both sides by - 3 )

x = 2

Substitute x = 2 into (2)

y = - 8 + 15 = 7

Coordinates of vertex = (2, 7 )

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step-by-step explanation: