What is the value of x?
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x = 9, y = 5

Step-by-step explanation:

This is an equilateral triangle, so all angles are the same:  60 degrees.

Then 7x - 3 = 60 and 11y + 5 = 60.

Consequently, 7x = 63 and x = 9; 11y = 55 and y = 5

12*c

step-by-step explanation:

x = ±sqrt(10)

step-by-step explanation:

5 - 2x² = -15

subtract 5 from each side

5-5 - 2x² = -15-5

-2x^2   = -20

divide by -2 on each side

-2x^2   /-2= -20/-2

x^2 =10

take the square root on each side

sqrt(x^2 )=±sqrt(10)

x = ±sqrt(10)

check:

5 - 2x² = -15

+sqrt(10)

5 - 2(sqrt(10))² = -15

5 -2(10) = -15

5 -20 = -15

-15 = -15

-sqrt(10)

5 - 2(-sqrt(10))² = -15

5 -2(10) = -15

5 -20 = -15

-15 = -15