Correct Answer - Option 2 : 45°

**Given:**

The angle between two lines 3x + y - 7 = 0 and x + 2y + 9 = 0

**Formula used:**

Tanθ = (m_{2} - m_{1})/(1 + m_{1}m_{2})

y_{1} = m_{1}x + c & y_{2} = m_{2}x + c

**Calculation:**

According to the question,

3x + y - 7 = 0

⇒ y = - 3x + 7

⇒ m_{1} = -3

x + 2y + 9 = 0

⇒ y = -x/2 - 9/2

⇒ m_{2} = - 1/2

Tanθ = (m2 - m1)/(1 + m1m2)

⇒ (-1/2 - (-3))/(1 + (-3)(-1/2))

⇒ 5/3/5/3

⇒ Tanθ = 1

⇒ θ = 45^{o}

**∴ The angle between two lines 3x + y - 7 = 0 and x + 2y + 9 = 0 will be 45**^{o}.