To solve the problem, we need to find the centre of a circle when the endpoints of its diameter are given as (1, 2) and (7, –4).
1. Understanding the Concept:
The centre of a circle is the midpoint of the diameter. If the endpoints of the diameter are \( (x_1, y_1) \) and \( (x_2, y_2) \), then the midpoint is given by:
\[
\left( \frac{x_1 + x_2}{2}, \frac{y_1 + y_2}{2} \right)
\]
2. Substitute the values:
Given points: \( (1, 2) \) and \( (7, -4) \)
\[
x = \frac{1 + 7}{2} = \frac{8}{2} = 4
\]
\[
y = \frac{2 + (-4)}{2} = \frac{-2}{2} = -1
\]
3. Calculate the Coordinates of the Centre:
The centre of the circle is at \( (4, -1) \).
Final Answer:
The correct answer is option (B): (4, –1).
The equation of a circle which touches the straight lines $x + y = 2$, $x - y = 2$ and also touches the circle $x^2 + y^2 = 1$ is: