Completing the square

What is the first step to solving THIS equation by completing the square?
a² + 10a + 21 = 0

• Set the equation equal to zero
• Divide 10 by 2 and add the result to both sides
• Add a² and 10a together
• Subtract the 21

What value of c would make this a perfect sqaure trinomial?
x² +8x + c

• 4
• 16
• 64
• -16

Complete the Square
x² + 6x = 5

• (x + 3)² = 5
• (x + 6)² = 9
• (x + 3)² = 14
• (x + 6)² = 14

Solve by completing the square:
k² − 12k + 23 = 0

• {6 + √13, 6 - √13}
• {-6 + √13, -6 - √13}
• {6 + √59, 6 - √59}
• {-6 + √59, -6 - √59}

Solve by completing the square.
y² + 10y = -9

• 1 and -12
• -1 and -9
• 1 and -9
• 1 and -1

Solve by completing the square.
x² +12x = 5

• X = 6 + √41 or  6 − √41
• X= 35 or 47
• X = −6 + √41 or  −6 − √41
• X = √35 or √47