Circle equations Y9 center at origin

What is the equation of this circle?

• x+y=1
• x+y²=1
• x²+y=1
• x²+y²=1

What is the equation of this circle?

• x²+y²=4 
• x+y=4
• x+y=2
• x²+y²=2

Find the center of the circle if the endpoints of a diameter are
 (3, -2) and (7, 6).

• (5, 2)
• (10,4)
• (0, 0)
• (-2, 4)

In the equation
x²+y²=16, the radius of the circle is...

• 0
• 2
• 4
• 16

In the equation
x²+y²=49, the radius of the circle is...

• 49
• 7
• (0,0)
• 0

In the equation
x²+y²=36, the radius of the circle is...

• 6
• 36
• 3
• (0,0)

In the equation
x²+y²=49, the center of the circle is...

• (0,0)
• (0,7)
• (7,0)
• (7,7)

In the equation
x²+y²=16, the center of the circle is...

• (4,0)
• (0,4)
• (0,0)
• (4,4)

Write the equation of the circle with  center (0,0) and radius 3

• x²+y²=4
• x²+y²=81
• x²+y²=9
• x²+y²=(0,0)

What is the center of the circle with equation
x² + y² = 1?

• (1, 1)
• (0, 0)
• not enough information
• (1, 0)