Which equation represents a circle?

C

Step-by-step explanation:

The equation of a circle centred at the origin is

x² + y² = r² ← r is the radius

Consider

+ = 1, that is

+ = 1

Multiply through by 4

x² + y² = 4 ← equation of circle

This is the equation of a circle centred at the origin with radius 2

x = 10.1

step-by-step explanation:

all of the angles of a tirangle add up to 180º

180 - 65 = 115 (since we already know the value of one angle)

(2x + 7) + (8x + 7) = 115

(combins like terms) 10x + 14 = 115

(isolate the variable subtract 14 from both sides): 10x = 101

(find the variable divide both sides by 10): x = 101/10

x = 10.1

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step-by-step explanation: