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25

Step-by-step explanation:

The angle of an arc is the same as the central angle. MarcCD is the same as the central angle COD which is given as 130o.

That means there are 50 degrees left for COA and DOA and because the chord and the diameter are equal, COA = DOA

That means that COA is 1/2 what is left over from 180 when 130 is subtracted from it.

1/2 * 50 = 25

The answer is A 25.

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

the first one is x^2+2x+2

the second one is x^2+4

the last one is x^2-4x+8