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Find the equation of the circle, coordinates of C, and the equation of tangent AB.

Mathematics

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6 steps
  1. Determine the equation of the circle (3.1).

    The center of the circle is M(−2;3)M(-2; 3), so a=−2a = -2 and b=3b = 3.
    The circle passes through point A(1;−1)A(1; -1).
    The radius squared, r2r^2, is the distance squared between M and A:

    r2=(xA−xM)2+(yA−yM)2r^2 = (x_A - x_M)^2 + (y_A - y_M)^2 r2=(1−(−2))2+(−1−3)2r^2 = (1 - (-2))^2 + (-1 - 3)^2 r2=(3)2+(−4)2r^2 = (3)^2 + (-4)^2 r2=9+16r^2 = 9 + 16 r2=25r^2 = 25

    The equation of the circle is:

    (x−(−2))2+(y−3)2=25(x - (-2))^2 + (y - 3)^2 = 25 (x+2)2+(y−3)2=25\boxed{(x + 2)^2 + (y - 3)^2 = 25}
  2. Write down the coordinates of C (3.2).

    The center of the circle is M(−2;3)M(-2; 3) and the radius is r=25=5r = \sqrt{25} = 5.
    The line BC is parallel to the y-axis, meaning it is a vertical line.
    Since BC is tangent to the circle at C, the radius MC is perpendicular to BC.
    As BC is vertical, MC must be horizontal. This means the y-coordinate of C is the same as the y-coordinate of M, which is 3.
    From the diagram, C is to the left of M. The x-coordinate of C is xM−rx_M - r.

    xC=−2−5=−7x_C = -2 - 5 = -7

    The coordinates of C are:

    C(−7;3)\boxed{C(-7; 3)}
  3. Determine the equation of the tangent AB (3.3).

    The tangent AB touches the circle at A(1;−1)A(1; -1). The center is M(−2;3)M(-2; 3).
    First, find the gradient of the radius MA:

    mMA=yA−yMxA−xM=−1−31−(−2)=−43m_{MA} = \frac{y_A - y_M}{x_A - x_M} = \frac{-1 - 3}{1 - (-2)} = \frac{-4}{3}

    Since the tangent AB is perpendicular to the radius MA, the product of their gradients is -1:

    mAB⋅mMA=−1m_{AB} \cdot m_{MA} = -1 mAB⋅(−43)=−1m_{AB} \cdot \left(\frac{-4}{3}\right) = -1 mAB=34m_{AB} = \frac{3}{4}

    Now use the point-slope form y−y1=m(x−x1)y - y_1 = m(x - x_1) with point A(1;−1)A(1; -1) and mAB=34m_{AB} = \frac{3}{4}:

    y−(−1)=34(x−1)y - (-1) = \frac{3}{4}(x - 1) y+1=34x−34y + 1 = \frac{3}{4}x - \frac{3}{4} y=34x−34−1y = \frac{3}{4}x - \frac{3}{4} - 1 y=34x−74y = \frac{3}{4}x - \frac{7}{4}

    The equation of the tangent AB is:

    y=34x−74\boxed{y = \frac{3}{4}x - \frac{7}{4}}
  4. Determine the length of BC (3.4).

    From Step 2, C(−7;3)C(-7; 3).
    The line BC is a vertical line, so the x-coordinate of B is the same as C, which is -7.
    Point B is the intersection of the tangent AB (from Step 3) and the line x=−7x = -7.
    Substitute x=−7x = -7 into the equation of AB:

    yB=34(−7)−74y_B = \frac{3}{4}(-7) - \frac{7}{4} yB=−214−74y_B = \frac{-21}{4} - \frac{7}{4} yB=−284y_B = \frac{-28}{4} yB=−7y_B = -7

    So, B(−7;−7)B(-7; -7).
    The length of BC is the absolute difference in their y-coordinates:

    BC=∣yB−yC∣=∣−7−3∣=∣−10∣=10BC = |y_B - y_C| = |-7 - 3| = |-10| = 10

    The length of BC is:

    10 units\boxed{10 \text{ units}}
  5. Determine the equation of the circle centred at A that has the x- and y-axis as tangents (3.5).

    The center of this new circle is A(1;−1)A(1; -1).
    For a circle to be tangent to both the x-axis and the y-axis, its radius must be equal to the absolute value of its x-coordinate and y-coordinate.
    Radius r=∣xA∣=∣1∣=1r = |x_A| = |1| = 1.
    Radius r=∣yA∣=∣−1∣=1r = |y_A| = |-1| = 1.
    So, the radius of this circle is r=1r = 1.
    The equation of the circle is (x−xA)2+(y−yA)2=r2(x - x_A)^2 + (y - y_A)^2 = r^2:

    (x−1)2+(y−(−1))2=12(x - 1)^2 + (y - (-1))^2 = 1^2 (x−1)2+(y+1)2=1(x - 1)^2 + (y + 1)^2 = 1

    The equation of the circle is:

    (x−1)2+(y+1)2=1\boxed{(x - 1)^2 + (y + 1)^2 = 1}
  6. Determine all possible values of p (3.6).

    The original circle (Circle M) has center M(−2;3)M(-2; 3) and radius rM=5r_M = 5 (from Step 1).
    The new circle (Circle N) has center $N(p

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