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When circle P is plotted on a coordinate plane, the equation of the diameter that passes through point Q on the circle is [tex]y = 4x + 2[/tex]. Which statement describes the equation of a line that is tangent to circle P at point Q?

A. The slope of the tangent line is -4.
B. The slope of the tangent line is [tex]\frac{1}{4}[/tex].
C. The slope of the tangent line is 4.
D. The slope of the tangent line is [tex]-\frac{1}{4}[/tex].

Sagot :

To find the slope of the tangent line to the circle [tex]\( P \)[/tex] at point [tex]\( Q \)[/tex], we need to use the fact that the tangent line is perpendicular to the radius (or diameter) at the point of tangency. Given that the diameter of the circle passing through [tex]\( Q \)[/tex] has the equation [tex]\( y = 4x + 2 \)[/tex], we can determine the slope of the diameter and subsequently the slope of the tangent line.

1. Identify the slope of the diameter:
The given equation of the diameter line is [tex]\( y = 4x + 2 \)[/tex]. The general form of a linear equation is [tex]\( y = mx + b \)[/tex], where [tex]\( m \)[/tex] represents the slope. Comparing this general form to our given equation, we see that the slope of the diameter ([tex]\( m \)[/tex]) is 4.

2. Determine the slope of the tangent line:
A fundamental property of perpendicular lines in analytic geometry is that the product of their slopes is [tex]\(-1\)[/tex]. Let's denote the slope of the tangent line as [tex]\( m_t \)[/tex]. Then, we use the condition of perpendicularity:

[tex]\[ \text{slope of diameter} \times \text{slope of tangent line} = -1 \][/tex]

Substituting the known slope of the diameter into this equation gives:

[tex]\[ 4 \times m_t = -1 \][/tex]

3. Solve for the slope of the tangent line:

[tex]\[ m_t = \frac{-1}{4} \][/tex]

Thus, the slope of the tangent line to circle [tex]\( P \)[/tex] at point [tex]\( Q \)[/tex] is [tex]\(-\frac{1}{4}\)[/tex].

So, the correct statement is:

D. The slope of the tangent line is [tex]\(-\frac{1}{4}\)[/tex].